Can't create itunesconnect sandbox tester

Question

I'm stuck with itunesconnect. For testing my in-app purchase code of an iOS app I try to create a sandbox tester account, but all I get is "An unknown error has occurred." As email address I use a gmail address like "[email protected]" which is not an existing Apple ID.
The only weird thing I can see is the date-of-birth thing where I can specify month and day only (no year).
Has anyone experienced the same problem? Is that a problem inside itunesconnect or what can I do here? Any help is appreciated.
Andreas

Answer 1

I had to use at least 1 upper case, 1 special char (like @), 1 punctuation mark and 1 lower case and be at least 8 digits long

I was getting simply 'This field is invalid' in the password when submitting - no guidance at all as to what was wrong - great UX Apple