Shops can save coupon identifiers containing characters the Square API rejects (confirmed: %). CS accepts the code with no validation warning. When a customer applies it at checkout, the Square API call fails and card payment is rejected. Store credit payments still succeed, so the failure presents as payment-method- or app-specific rather than coupon-related. No error surfaces that points at the coupon.

We’d like to get some kind of validation warning when the coupons are being created that contain characters that will be rejected by the Square API - could also surface some kind of more detailed error message stating that the issue is with the coupon code being used.