You will need to obtain your key from the BeamMP Keymaster site
Click the Keys option on the left-hand side of the website
Click the Green [+] icon to create a new key
Copy the key you have created.
Login to your server's control panel
Navigate to your BeamMP server.
Stop your server if it is running.
Click the Configuration Files option.
Click the Config Editor icon for the ServerConfig.toml
Paste your key in the License key setting
Click Save.