I feel like you're going about this the wrong way, you should ask the creator of the button, prior to any implementation, the questions if it fundamentally relies on them being in the right country and having registered for Stripe, something like this:

I feel like you're going about this the wrong way, you should ask the creator of the button, prior to any implementation, the questions if it fundamentally relies on them being in the right country and having registered for Stripe, something like this:

This prevents them from placing a button that potentially would not work, on their site in the first place.

Now, it's not clear from what you have said as to what the workaround is if they don't have a Stripe account or is the proviso to use your service that they must have one? These details would form part of the solution.