Either
with your 6-digit customer number - 3-digit store number
e.g. 059219-000
If you have only one store - your store number is always 000
If your customer number does not have 6 digits - fill in the front 0en on
your customer number can be found on every bill

or

with the deposited e-mail address
Ex max.mustermann@t-online.de
This only works as long as your e-mail address is only entered on a customer number in our system is.