After applying the 8.1.1 update, invoice payment attempts via the client area using a tokenised payment gateway may to encounter an error condition in specific circumstances.

The client will see errors upon submitting payment:

•        You did not enter your first name.
•        You did not enter your last name.
•        You did not enter your address (line 1).
•        You did not enter your city.
•        You did not enter your state.
•        You did not enter your postcode.
•        You did not enter your phone number.

A member of staff clicks "Attempt Capture" on the invoice in the admin area.                        

Please apply the 8.1.2 Maintenance Release via the Utilities > Update WHMCS page.

A hotfix has been created for 8.1.1 only to resolve the root cause:

https://whmcs.community/files/file/160-module-7591-manual-tokenised-gateway-payments/