PBA allows to configure masks in Payment System properties, they allow validating credit card numbers and bank account numbers. Provider may manage masks in the PBA Provider Control Panel at Configuration Director > E-Commerce Settings > Payment Systems > select Payment System > Masks tab.
As Provider I want to to specify mask to accept letters as well as digits.
Currently, there is no such functionality in PBA, mask can only consist of numbers and 'I' signs which mean any digit.
The required functionality is going to be implemented in the future versions of PBA is scope of the request PBA-50214.