In Gensco, Inc. v. Transformaciones Metalurgicias Especiales, S.A., 666 S.W.2d 549, 554 (Tex. App.--Houston 14th Dist. 1984, writ dism'd), the court of appeals concluded that copies of invoices sent by the plaintiff to the defendant, coupled with the defendant's responses to requests for admission in which the defendant admitted that it had accepted the goods, that the amounts reflected in the invoices were the agreed prices, and that it had not paid the full purchase price under any of the invoices, were sufficient to establish that the plaintiff had presented its claim to the defendant under the predecessor statute to section 38.002 of the Texas Civil Practice and Remedies Code. 666 S.W.2d at 552, 554.
In that case, the invoices themselves constituted evidence of a request for payment by the plaintiff, and the defendant's admissions established that the invoices contained the agreed upon prices and remained unpaid. See id.