Dear all, is it possible to blocking a number of characters in a text are

One way is to check the character length after form submission, ie in the process, and return to same form with an error that character length is higher if required.
Second method, is to use java script validation. This will not work on mobile or tempo forms.

Hi . . There is one other way .
You can use masking for that particular text field .
forum.appian.com/.../Text_Form_Component
Hopefully it will help.

Alternatively, if you are using 7.4 you can use SAIL forms to achieve the validation directly on the screen without validating after form submission (available in Tempo and mobile).

Masking is also not available on tempo or mobile.

forum.appian.com/.../SAIL_Recipes