Issue creating user with API

Hello, I've had a fully functional tool I've developed that with other functions include creating accounts to our Shiftplanning domain.

It has been working perfectly up until now when I always get the error:
User not created because of an error:
The input is not between '0' and '12', inclusively: $email

It doesn't matter what I fill out as email, it still throws this error.

Do you know any possible solutions for this?

Best regards,
Adam ÅKerman