Turning Account Receivables into a digital currency

How to hold a client to pay without a formal invoice? a promise isn't worth shit especially from a client in another country...

What if that client can issue you a formal "I Owe U" with terms of service, and those IoU's are shared publicly for all the world to see!

What if that client can issue that IoU on social media by just saying saying the word IoU while talking to you!

Who wants to brain storm this further?