Facebook needs to put something in their terms of service saying:
If you are using our service in any way to contact a client of yours who owes you money, you agree to forgive the debt in the entirety.
If you are using our service in any way to contact a client of yours who owes you money, you agree to forgive the debt in the entirety.
This is not the type of debt collector than can provide the promissory note or judgement documentation.