Details:

While I dislike and generally avoid KYC off-ramps, preferring p2p exchange whenever it's feasible, for reasons of convenience I did use this one on a few occasions. The first few transactions to fund a USD Mastercard went fine, but a few weeks ago their support desk refused to credit a couple of thousands USD worth of Bitcoin deposit, and they are currently refusing to give me back my money either. The "condition" they require, in order to return the loot, is an impossible chainanal challenge: giving them on-chain "proof of origin" of any single output involved in the tx graph of my funding transaction. My suspicion is that the "task" is intentionally designed to be impossible to comply with, in order to rug-pull users.

I'll keep you updated in the coming weeks.