@Mike_Chan I think it’s quite easy somehow but also difficult. First thing, you must have specific user IDs, email etc stored in Firebase, when user request pass code you must approve that payment made was a successful, then send the pass code using the store user data to deliver the code the right user, then use when Firebase database data changed block +itool for the specific user, notify them when the code was sent to user email, [FREE] Email OTP Verification[UNLIMITED]
Sorry maybe I made more difficult now
But it’s 100% possible if you have user IDs in your Firebase