The same issue can happen with Stripe.. They approve accounts before doing underwriting, once you hit a threshold your account is reviewed for underwriting, funds will be withheld, usually a 'rolling reserve of % of last X days of transactions' sometimes it's more. :(
I'm not sure of your situation and I'm not a lawyer, but you could research forming a US corporation as a foreign citizen. Stripe offers such a service called 'atlas'. While I've never used them for that, it may be a good source of information for you.
