Error 'one of the parameters is not of the type Positive

I was checking this new extension and bumped into an issue. It is either because I am not doing it correctly. (Then I hope you can explain to me what I should do.) Or there is a bug.

I used my own test environment (CiviCRM 5.34 / Drupal 7). Language is Dutch. See attachment 1 to show you what I tried to do and at what moment I got the error. 1._One_of_the_Parameters_is_not_of_the_type_Positive

Despite the error it has added the field, but when I want to add a value I also get a back trace (see attachment 2)