"Enter the four digit code present in the last recharge"


In the process to create an account before scanning the credit card we have the question (in French) "Entrez le code à quatre chiffre présent dans la derrière recharge"
it follows : "il figurera sur votre relevé pour votre Mastercard xxxx sous la forme "Revolut1234*"
But What is this code ?
For me, except for the credit card code, the only code with four digits is the one used to become identified with the apps.
You have a solution ?