Solutio Indebiti

Undue payment (solutio indebiti) occurred when a person, acting under a mistaken belief, transferred money or some other thing to another or discharged another's obligation in settlement of a non-existing debt.^[869] In such a case, the law laid a duty of restitution upon the person who received payment.

Recovery of a payment made without being due could be obtained by means of a special personal action, known as condictio indebiti?⁰⁰ For the successful institu­tion of this action the plaintiff had to prove that he had bona fide erred and had performed while labouring under a mistake (per errorem).^{[870] style='font-size:9.5pt;font-family: "Times New Roman",serif;color:black;font-weight:bold'>[871]} If he had tendered an undue payment knowingly, it was considered that he had made a donation (and thus he could not reclaim it).^[872] On the other hand, the person who received the money or other property also had to believe, bona fide, that the performance was due to him—otherwise he would be held to have committed theft (furtum).^[873] Moreover, ownership must have been transferred by one of the derivative modes of acquisi- tion.^[874] Finally, as it is obvious, there had to be no existing debt.

4.8.3