Can't process Stripe payment

On my Bubble site I tried to run a test transaction. I have a Stripe account with API keys entered for the company/Bubble site, which is a marketplace. Then I also created a seller/instructor Stripe account. But when I try to execute a transaction with the instructor, I get this error:

“Sorry, this seller cannot accept payments right now due to a temporary error. Please try again later.”

I talked to Stripe support, and they thought that maybe I needed to use an Express account?

“If the Platform was set up to create Express or Custom accounts for their Connected accounts then they would not need to put in their own API keys as this would all be configured in the account setup/Oauth process.”

In any case, the seller Stripe account that is being used for the instructor is fully set up as far as Stripe is concerned. So the problem is on the Bubble side.

I am at a loss as to what to try next.

I have the same problem. Did you find a solution?