ERROR: Couldn’t register you… please contact the webmaster !

@naderi9

You have paid for support with your theme, so you should ask them :
https://www.appthemes.com/themes/classipress/

or read the topics in their forums :
https://forums.appthemes.com/search.php?searchid=108782

there are docs referring to this as well :
https://docs.appthemes.com/classipress-4-x/wordpress-settings-classipress-4-x/

Thank you @corrinarusso
I activated default wordpress theme (2020 ), the problem didn’t resolve

@naderi9

Do you have reCaptcha enabled, without using the Public and Private keys?
Have you set a Terms of Service to be required, but do not provide the checkbox?
Did you assign these pages under your General Options :
Register Page
Login Page
Account Page
Logout Page
Lost Password Page
Do you have another other plugins installed ?