There are two issues. One is that each developer has the power to change the payment method for their games. It's a bit long to explain in detail now, but basically, some games can be purchased with credit cards and others only with PayPal, but this depends on the developer.
Recently, due to an issue between payment platforms and NSFW games, I believe credit cards cannot be used with games marked as NSFW.
Regarding your issue, one suggestion is to use a browser that supports different profiles, so you can't log into Itch from your business profile and thus avoid inadvertent errors (just a suggestion).