Hi,
My OP was asking about possibly a broken sandbox credit card support on your end but I remembered that I had the same issue a while ago (see https://developer.squareup.com/forums/t/sandbox-card-4111-1111-1111-1111-does-not-work-anymore)
It would be good to unify the acceptance of test email addresses like [email protected] across your APIs (accept everywhere or reject everywhere).
Right now I can create a Square customer using this email address, but I’m unable to process any payment with it (eg when using Subscriptions).
All my best.