Happened to me with Paypal. Small amount, just wanted to try out the feature. Was impossible to get the bitcoin out (self-custodial wallet, fresh addresses, site just threw error messages), support gave the same answers as in the post (security, for my own protection) and offered no solution, had to sell the bitcoin again and left the platform. Good to only keep minimal amounts on platforms and do test-runs before doing anything with even slightly larger amounts.