Debt contract

Not asking for legal advice here, but there is a known thing within kink circles of a debt contract, where someone puts them into debt via a contract to another person. Currently it is very much in the mental space as it is pretty much known that these debt contracts are not enforcable by law etc.

Is there a way of making it legal? As assume a credit card contract is also a type of debt contract, where you commit to paying the minimum terms etc, and wondered why a debt contract between two people couldnt be made to be legal?

Many Thanks

Daz