open terminal, move to your docroot and run following command
composer require cryptoworxx/oxid-cnovationpay
After that, just activate the module in the Oxid backend and clear the cache
Once the plugin is installed, you need to get an API token to connect it to the CNovation-Pay ecosystem. You may generate a new token in your portal account or you can simply click on the "?" and then on "get access now" Link on the module config screen:
A new windows opens and leads you to the process of generating an API Token.
Copy that token, paste it into the module config window and save