WHMCS provisioning problem - dont create the sites

Hi i installed the whmcs provisioning plugin, and followed the instructions, seems everything is fine except one thing: the site creation is fail.

The user can register to whmcs, and place the order for the site - i set up "free" for testing - it give the domain, and title field, then place the order, i receive the email and i see in whmcs the order as "pending" (but i set up the automation to - Automatically setup the product as soon as an order is placed) - Ok so its dont created automatically, but when go into the products and services and aprove the order at whmcs admin - there is nothing happens - no site is created - when i hit the create button i get the error message: Module Command Error
: Is not a valid domain name, alphanumeric and "-" only: - Also i see that the domain name field is empty.

I want to use only per subdirectory style of this site so mydomain.com/sitename, dont wanna use any subdomains or mapping.

How shoud i set up the system to fix those issues ?

Thank you for help