Flow NFTs purchase/sell mechanism

Hey everyone,
one important question: if you mint your own NFTs, sell them and accept payments via Stripe / fiat (this would mean that the actual purchase amount would not be stored/processed on the Flow blockchain - only the NFT token transfer from one account to another) is that illegal? Is there anything special to consider here?
I know that Dapper is using the DUC (Dapper Utility Coin) on NBA Top Shot for, I guess, the same reason.

It is not illegal, the problem is selling some Xcoin to user, that’s why Dapper is using DUC

I don’t think thats illegal, but it’s effectively not an NFT if payments are made via stripe. You are right when you say, “this would mean that the actual purchase amount would not be stored/processed on the Flow blockchain”.

Tnx @bluesign & @Theo - does this mean that we need our own fungible token for our marketplace?
Is there somewhere a good explanation of the NBA Top Shot business model: fees etc.?