ACCION IN REM VERSO:
Action for recovery of what has been paid without just cause
1. Defendant has been enriched
2. Plaintiff suffered a loss
3. Enrichment of defendant is without just or legal ground
4. Plaintiff has no other action based on contract, quasi contract, crime or quasi-delict
Distinguished from solutio indebeti: Mistake is an essential element in solutio indebeti but not in accion in rem verso.