Here is simple install documentation for Free WemX billing module
Download the module files from here
Import all files to /var/www/pterodactyl folder on your server
Run: php artisan billing:install stable in directory /var/www/pterodactyl
When it asks you for license type: wemxcloud and press enter and wait for installation to finish
When is it done without errors, type yarn build:production in /var/www/pterodactyl
Refresh your site and you will get installed premium version of billing module 3.0