That which one has given, knowing it not to be due, with the intention of redemanding it, he cannot recover back.

Explanation

(English-origin maxim.) One who knowingly pays what is not owed, intending to demand it back later, cannot recover — the deliberate payment with knowledge forecloses the claim for restitution.

Where this applies

• A man knowingly overpays his rent by $200 each month planning to demand it back later, but the court refuses to let him recover because he paid voluntarily with full knowledge.
• A customer deliberately tips a waiter $500 intending to sue for the money back as a test case, but the court holds that the knowing overpayment cannot be reclaimed.
• A business pays a vendor's inflated invoice without protest, planning to demand a refund later, but the court says a knowing voluntary payment bars recovery.