I have background here and can take a pretty good guess at what happened. You used a Brex card, which Google sees as a “privacy card.” These are often used by scammers trying to circumvent Google blocking their credit card account numbers.

The solution here is to never use a hidden or “privacy” card number with Google, although of course Google will never tell you that or confirm or deny this. I only know this due to working with clients in this area.

You can try removing that card and adding a regular hard card number and asking for a reinstatement again, but it may be too late for this account.

Hopefully this helps folks reading this to not make the same mistake (although it’s incredibly frustrating that stuff like this has to be learned by trial and error or knowledge from those of us who have dealt with this previously.)