RE I tried to add license key but it says “License check response returned NULL.” … The issue with the license key is solved.
The web host was having uptime issues which was causing some failures. This should mostly be resolved now. Apologies for the trouble!
RE: I tried to submit a listing as a user but it doesn’t work.
I just tested on your site. It seems your web host or your sites configuration is blocking access to the
../wp-admin/admin-ajax.php file. This file is used by WP and plugins to process AJAX requests. You’ll need to remove the block in order for this to correctly function.
Hope this helps, let me know.