The condictio indebiti is an action in civil (Roman) law whereby a plaintiff may recover what he has paid the defendant by mistake; such mistaken payment is known as solutio indebiti. This action does not lie

1. if the sum was due ex aequitate, or by a natural obligation;
2. if he who made the payment knew that nothing was due, for qui consulto dat quod non debet, praesumitur donare (who gives purposely what he does not owe, is presumed to make a gift).^[1][2][3]

The action is extant in civil (Roman) or hybrid law regimes, e.g. Norway,^[4] South Africa and Scotland .^[5]

• Condictio causa data causa non secuta

§ 812 I 1 1. Alt BGB (German Civil Code)

• Outlines of Roman Law By Thomas Whitcombe Greene
• Roman-Frisian law of the 17th and 18th century By J. H. A. Lokin, Frits Brandsma, C. J. H. Jansen
• Imperatoris Iustiniani Institutionum Libri Quattuor By John Baron Moyle, Justinian
• "The evolution of the law of unjustified enrichment"