whether the quantum of RM205,023.46 was proved, in particular in the light of the concession of PW1 concerning a missing invoice. [19] Underlying all four is the single, controlling question on a first appeal of this nature: whether the findings of the trial court are so against the weight of the evidence, or so lacking in judicial appreciation of it, that this court is entitled to interfere. F. THE GOVERNING PRINCIPLES [20] This appeal is a rehearing on the record. It is settled that an appellate court will not lightly disturb the findings of fact of a trial court which has had the advantage of seeing and hearing the witnesses. Intervention is warranted only where the trial court is shown to have been plainly wrong, in the sense of having reached a conclusion that no reasonable tribunal, properly directing itself, could have reached, or where there has been a failure of judicial appreciation of the evidence. Those principles are conveniently stated in Arab-Malaysian Finance Bhd v Steven Phoa Cheng Loon & Ors and other appeals [2003] 1 MLJ 567 (CA), and in Lee Ing Chin @ Lee Teck Seng & Ors v Gan Yook Chin & Anor [2003] 2 MLJ 97 (CA), both of which were relied upon before me. The enquiry is therefore not whether I would have made the same findings, but whether the findings made were reasonably open on the evidence. [21] Two further propositions are engaged, and only to the extent the grounds require. First, a contract of this kind need not be reduced to writing; it may be formed by conduct, provided the elements of proposal, acceptance and consideration in section 2 of the Contracts Act 1950 are present. The exchange of mutual promises is itself good consideration, even while executory: Wong Hon Leong David v Noorazman bin Adnan [1995] 3 MLJ 283 (CA). Secondly, the legal burden of proving the claim, including its quantum, rests on the respondent throughout, under section 101(1) of the Evidence Act 1950, although the evidential burden may shift in the course of the trial as the evidence unfolds. [22] Beyond these, the law was not seriously in contest. The dispute is as to the application of settled principles to the facts found, and it is to that application that I now turn. [23] A further principle is engaged by the respondent's submission in-reply, and it is convenient to state it here. On a first appeal of this nature, this court will not ordinarily permit a party to raise a point that was not taken before the trial court; and, in particular, a party who allowed evidence to be admitted at trial without objection will not ordinarily be permitted to challenge its admissibility for the first time on appeal. The reception of fresh evidence on appeal is separately restricted by Order 55 rule 7 of the Rules of Court 2012, which admits it only where the evidence could not, with reasonable diligence, have been obtained for use at the trial, and where it would, if true, have had or have been likely to have a determining influence upon the decision of the court below. Those conditions are to the same effect as the conditions stated in Ladd v Marshall [1954] 1 WLR 1489, which the Federal Court applied in Lam Soon Cannery Co v Hooper & Co [1965] 2 MLJ 148, where the court, treating the conditions as cumulative, held that, the evidence sought to be adduced having been at all material times in the possession of the party seeking to use it, it would be wrong to exercise the discretion in that party's favour. I observe, however, that those provisions are directed at the reception of fresh evidence, and not at the raising of a fresh argument upon evidence already on the record. To the extent that the respondent deploys them against an argument of the latter kind, they are engaged only by analogy; the operative bar in such a case is the rule against the raising of new points on appeal, to which I have referred. G. ANALYSIS AND DETERMINATION Whether There Was A Contractual Nexus Between The Appellant And The Respondent [24] The first ground asserts an absence of privity. It was said that the respondent produced no written service agreement, no purchase order and no letter of appointment, and that without such foundational documents no contract could be established. [25] The contention rests upon a premise the law does not accept, namely that a contract for services of this kind must be evidenced in writing. It need not. Section 2 of the Contracts Act 1950 recognises that an agreement arises where a proposal is accepted and supported by consideration, and these may be manifested by conduct. Where one party renders services and issues invoices for them, and the other receives those services and the invoices without protest, a court may properly find a proposal and an acceptance, the services on the one side and the obligation to pay on the other constituting the consideration. That is the analysis adopted in Wong Hon Leong David, where the Court of Appeal held that the exchange of mutual promises, although executory, was good consideration giving rise to a binding agreement. [26] On the evidence before the Sessions Court, that analysis was open. The invoices, spanning the period from April 2019, were issued in the respondent's name and were, in the main, either signed or impressed with the chop of the Executive Housekeeper of Mudzaffar Hotel the appellant's own establishment. The course of dealing was corroborated by the appellant's internal memorandum of 8 August 2020, which acknowledged an outstanding balance and recorded an agreed schedule of repayment. The finding that a contract had been formed by conduct was therefore not merely permissible; it was the natural inference from the documents. There is no basis upon which I could characterise it as plainly wrong. [27] Reliance on Tee Siew Kai (liquidators for Merger Acceptance Sdn Bhd (in liquidation)) v Machang Indah Development Sdn Bhd (in liquidation) (previously known as Rakyat Corp Sdn Bhd) [2020] 6 MLJ 168 (FC) does not assist the appellant. That decision concerned whether a claim had been brought against the wrong defendant there, a liquidator sued personally in respect of obligations of the company in liquidation. The proposition it yields, that a claim must be directed against the party against whom the cause of action in truth lies, is unexceptionable; but it presupposes the very question in issue here, namely against whom the cause of action lay. On the facts found, it lay against the appellant. The authority does not displace that finding; it depends upon it. Whether The Respondent Was The Proper Party To Sue: The Third-Party Contention [28] The second ground is the obverse of the first. It was contended that the appellant's dealings were exclusively with CNC Express Sdn Bhd, an independent third party, so that the respondent was a stranger to the arrangement and without standing to sue. There are two difficulties with that contention, each sufficient to dispose of it. [29] The first is one of pleading. A party is bound by the case it has pleaded, and may not advance on appeal a case materially different from that put to the trial court. The defence did not plead that CNC Express was an independent third party with whom alone the appellant had contracted. What it pleaded, at paragraph 6, was that the appellant had dealt at all material times only with "the Plaintiff's representative". A defence framed in terms of the respondent's own representative is not a defence of dealings with an unconnected stranger; it is, if anything, consistent with the respondent's case. The theory now advanced of a separate and unconnected contracting entity was not the case below, and the appellant cannot be permitted to recast its defence in this court. [30] The second difficulty is evidential. Even taken on its own merits, the contention was unsupported. SD1 asserted that the appellant dealt with "Puan Sarah" of CNC Express, but the appellant produced no agreement with CNC Express, no purchase order to CNC Express, and no record of any payment to CNC Express. Against that absence of proof stood the respondent's invoices, all issued in the respondent's name; the memorandum at page 46 of Bundle B, emanating from the appellant's own Executive Housekeeper, which described the creditor as "CNC Express Sdn Bhd (Best Sun Tech Sdn Bhd)"; and the memorandum at page 47 on the respondent's letterhead, issued by a director of the respondent, which coupled "Best Suntech" and "CNC Express" in the same manner. From these documents the Sessions Court inferred that the two names denoted the same source of supply, and that "Puan Sarah" acted for the respondent. That inference was one a reasonable tribunal could draw; the document originating from the appellant's own officer points directly to it. Once the respondent had adduced invoices in its own name, the evidential burden of displacing that inference lay on the appellant, and the appellant adduced nothing to discharge it. [31] Seascope Sdn Bhd v Syed Izhar bin Syed Syed Salleh [2006] 3 MLJ 756 (HC), also relied upon, was concerned with whether a valid acceptance had been communicated so as to conclude a contract. It establishes no more than that the party asserting a contract must prove it a burden discharged here by the conduct and documents already described. The authority does not carry the further argument that the respondent was a stranger to the dealings. [32] For these reasons the finding that the respondent was the proper party to sue was correct, and certainly not plainly wrong. Whether The Delivery And Receipt Of The Invoices Was Established [33] Before considering this ground upon its merits, I must address a threshold objection taken by the respondent. The respondent contends that, in so far as the appellant now impugns the admissibility or evidential value of the invoices including the contention that they were "self-generated" that challenge is not open to the appellant on appeal. It was not pleaded, the defence having put in issue only the existence of a contractual relationship and not the admissibility of the invoices; nor was it argued before the learned Sessions Court Judge. The respondent further submits, by reference to pages 14 to 20 of Part B of the Record of Appeal, that the invoices were tendered and admitted at trial without objection, the appellant having elected, when invited to object, to proceed instead to the cross-examination of the respondent's witness. [34] The principle relied upon is, in my view, sound. A party who stands by while evidence is admitted at trial, and takes no objection, will not ordinarily be permitted to challenge the admissibility of that evidence for the first time on appeal. The time to object is when the evidence is tendered, so that the trial court may rule upon the objection and the party adducing the evidence may, if so advised, cure any defect. A challenge of that character, raised only on appeal, was not ventilated below and is not properly open to the appellant. As to the respondent's reliance on Order 55 rule 7 of the Rules of Court 2012 and on Lam Soon Cannery Co v Hooper & Co, I have already observed that those provisions govern the reception of fresh evidence, whereas the appellant does not seek to adduce fresh evidence but to re-argue upon material — the notes of evidence — that formed part of the record and was in its possession throughout. The provisions are therefore engaged only by analogy; but the analogy, so far as it extends, tells against the appellant, for the rationale of the rule is precisely that a party ought not to be permitted to improve its position on appeal by deploying what was available to it at trial. Lest the appellant be thought shut out upon a technicality, however, I have in any event considered the ground upon its merits, and it fails there also, for the reasons that follow. [35] The third ground is that the respondent failed to prove delivery and receipt of its invoices. Emphasis was placed on the acceptances by PW1 in cross-examination that certain invoices those at pages 10,12 and 14 of Bundle B bore no chop or signature, that he could not name the individuals who had signed others, and that the "everyday forms" recording each collection of linen, and the "service reports" recording the work done, were not included in the bundle. [36] Those concessions were real, and the Sessions Court did not ignore them; it confronted them. Its reasoning was that, although some invoices were unsigned, the invoices in the main bore the chop of the Executive Housekeeper of Mudzaffar Hotel; that this raised a case calling for an answer; and that the appellant which did not deny that the chop was its own, and led no evidence to contradict receipt had failed to answer it. That reasoning is sound. A document bearing the recipient's own chop is evidence of its receipt, and in the absence of any challenge to the authenticity of the chop, or any competing account, the trial court was entitled to treat receipt as established. The respondent adds, and the record bears out, that in so far as a small number of invoices bore neither chop nor signature, its witness explained the position in evidence (at pages 31 to 32 of Part B of the Record of Appeal); the weight to be given to that explanation was a matter for the trial court, which was entitled to accept it. [37] The absence of the "everyday forms" and "service reports" does not alter that conclusion. Those documents go to the weight of the respondent's evidence, not to its admissibility, and their absence fell to be assessed against the evidence that was before the court: invoices in the respondent's name bearing the appellant's chop; the appellant's own acknowledgment of an outstanding balance in August 2020; the agreed schedule of repayment; and the part-payment of RM1,500 in August 2023. A trial court is not bound to reject a claim merely because the most complete conceivable record was not produced, where the evidence actually adduced, taken as a whole, establishes the matter on a balance of probabilities. The best evidence principle, reflected in section 64 of the Evidence Act 1950, requires that documents be proved by primary evidence; the primary documents relied upon the invoices were produced, and the principle does not require the production of every ancillary record in order to prove a receipt that is otherwise established. [38] I therefore see no error, still less a plain one, in the finding that the invoices were delivered to and received by the appellant. Whether The Quantum Of The Claim Was Proved [39] The fourth ground is the one on which the appellant placed its greatest weight, and it requires the most careful treatment. The complaint is that PW1 conceded under cross-examination that the pleaded sum of RM205,023.46 was "not the actual amount", because a constituent invoice, Invoice No. 1679, had been omitted from the bundle of documents. From that concession it was said to follow that the quantum was unproven, and the judgment for that precise sum unsafe. [40] The concession must be given its proper meaning, neither more nor less. Taken at its highest, it establishes that the bundle did not physically contain one of the invoices listed in the schedule pleaded at paragraph 5 of the statement of claim. It does not establish that the true debt was some lesser sum, and still less does it identify what that lesser sum might be. The significance of a missing invoice depends upon what the remaining evidence shows. [41] Here the remaining evidence was substantial, and not confined to the invoices. Three matters in particular supported the figure found. First, the appellant's own memorandum of 8 August 2020 acknowledged an outstanding balance of RM188,611.81 as at July 2020, and it was not disputed that services continued thereafter until 2021. Secondly, the respondent's email correspondence informed the appellant that the sum outstanding for the services rendered between 2019 and 2021 was RM206,523.46, and the appellant, far from disputing that figure, sought an extension of time and pleaded financial hardship occasioned by the pandemic. Thirdly, the appellant made a payment of RM1,500 on 14 August 2023. The arithmetic is instructive: the figure of RM206,523.46 stated in the correspondence, less the admitted payment of RM1,500, yields precisely RM205,023.46 — the sum for which judgment was given. The figure is thus not a bare assertion. It reconciles, to the sen, with the sum the appellant was itself told and did not contest, adjusted for the very payment the appellant made. [42] Against that body of evidence, the omission of a single invoice from the bundle could not be decisive. The legal burden of proving quantum remained on the respondent under section 101(1) of the Evidence Act 1950, but the evidential burden had plainly shifted. An appellant which has acknowledged a debt of RM188,611.81, watched it grow as services continued, been told the resulting figure, sought time rather than disputed it, and made a payment on account, must — if it asserts that the true sum is lower — produce something to show what the true sum is. The appellant pleaded that its own accounts disclosed no debt, yet those accounts were never produced. It led no evidence of any payment beyond those credited, and none of any waiver. In those circumstances the trial court was entitled to accept the reconciled figure of RM205,023.46. [43] I add this, for completeness and candour. The grounds of judgment record the sum, at certain points, as RM205,023.36, while elsewhere and in the pleaded schedule, the formal judgment and the operative order it appears as RM205,023.46. The variance is one of ten sen and is plainly a slip; the operative figure, fixed by the schedule and the order, is RM205,023.46. Nothing turns upon it, and it does not touch the safety of the finding. [44] The concession of PW1, weighed against the whole of the evidence, did not render the quantum unproven. The finding was open to the trial court and discloses no error warranting interference. H. THE AWARD OF COSTS BELOW [45] The memorandum of appeal also challenges the award of costs of RM7,000. Costs are a matter for the discretion of the trial court, and an appellate court will not interfere unless that discretion was exercised upon a wrong principle or is plainly wrong. No such error was demonstrated. The sum awarded is consistent with the scale for trials in the subordinate courts under Order 59 rule 23 of the Rules of Court 2012, and reflects a trial conducted over three days. There is no basis to disturb it. I. CONCLUSION [46] Standing back from the individual grounds, the appeal is in substance an invitation to retry the case upon the documents and to substitute a different view of the facts for that of the trial court. That is not the function of this court on a first appeal. The findings of the Sessions Court that a contract was formed by conduct, that the respondent was the proper party, that the invoices were received, and that the debt stood at RM205,023.46 were each reasonably open on the evidence; and the most serious of the appellant's points, the concession as to quantum, does not survive scrutiny when measured against the appellant's own acknowledgments and conduct. The conditions for appellate intervention identified in Arab-Malaysian Finance Bhd and Lee Ing Chin are not met. The further matters pressed in the respondent's submission-in-reply do not improve the appellant's position: the objection to the lateness of the appellant's written submission is, given the outcome, academic; and the attempt to challenge the admissibility of the invoices on appeal is, for the reasons I have given, not open to the appellant and in any event without merit. The appeal accordingly fails. J. ORDERS [47] I make the following orders: