Hi @datex,
Have you had a look at the post discussed previously (it should solve your issue):
Looking at your 8 digit integer requirement with a 0 at the beginning, maybe your constraint should be something like:
(regex(., '^[00000001-99999999]{8}$') and (. >= 00000001))
For further understanding on regex, please feel free to have a look at our support article Restricting Text Responses With Regular Expressions. There you should see a lot of day to day useful regex codes that could make your form building process easy.
