I am a current LA fitness member and I am trying to create an account on the mobile LA...

I am a current LA fitness member and I am trying to create an account on the mobile LA fitness app so that I can sign up for classes and look up the class schedules and I am currently at the step where the app is asking me to "enter the first * digits of the account used for your recurring fees." What does this mean? First * digits of my bank account number? Debit card number? LA fitness account number? I need some insight on what I am being asked to enter here please. I do not have anything else to add but I can not submit my inquiry unless I type at least *** characters which I feel I more than have but I guess I haven't because every time I click on "continue" I get the same message in red font reading "for better results, write at least *** characters" like I might as well be typing up a book here for Christ's sake. I hate technology.