Background.  Unjust enrichment  is an equitable theory of recovery holding that one who receives  benefits unjustly should make restitution for those benefits, and is not  dependent on the existence of a wrong. Bransom v. Standard Hardware, Inc.,  874 S.W.2d 919, 927 (Tex. App.--Fort Worth 1994, writ denied). A person  is unjustly enriched when he obtains a "benefit from another by fraud,  duress, or the taking of an undue advantage." Heldenfels Bros., Inc. v. City of Corpus Christi,  832 S.W.2d 39, 41 (Tex.1992).  It occurs when a person sought to be  charged has wrongfully secured a benefit or has passively received a  beenfit which would be unconscionable to retain. City of Corpus v. S.S. Smith & Sons Masonry, Inc.,  736 S.W.2d 247, 250 (Tex. App.--Corpus Christi 1987, writ denied).  Unjust enrichment characterizes the result or failure to make  restitution of benefits received under such circumstances as to give  rise to implied or quasi-contract to repay. Allen v. Berrey, 645 S.W.2d 550, 553 (Tex. App.--San Antonio 1982, writ ref'd n.r.e.).

Elements.  An unjust enrichment claim requires proof of the following elements: (1) that valuable services were rendered or materials furnished; (2) for the person sought to be charged; (3) which services and materials were accepted by the person sought to be charged, used, and enjoyed by that person; and (4) under such circumstances as reasonably notified the person sought to be charged that the plaintiff in performing such services was expecting to be paid by the person sought to be charged. Reveille Trucking, Inc. v. Lear Corp., No. 4:14-CV-511, 2017 WL 661521, at *13 (S.D. Tex. Feb. 17, 2017); Jupiter Enterprises, Inc v. Harrison, No. 05–00–01914–CV, 2002 WL 318305, at *3 (Tex. App.—Dallas Mar. 1, 2002). Generally, however, a plaintiff cannot recover under a theory of unjust enrichment where a valid contract covers the subject matter of the dispute. Id.

Statute of Limitations.  Unjust enrichment claim are governed by the two-year statute of limitations. Elledge v. Friberg-Cooper Water Supply Corp., 240 S.W.3d 869, 869 (Tex. 2007).