I would give 0 stars if I could…
The system is ultimately flawed. There is no way to change your username after signing up, and this issue led to my debit and credit cards being denied. The somewhat sarcastic “uh oh, there is a small issue with the payment process” is poking fun at people just trying to rely on a mobility solution for their needs. It's hard to understand how German companies repeatedly fail in viable solutions for international guests… a real pity! In its current form, unusable!