When you have your ONLYOFFICE Docs installed on Cloudron, go to My Apps, find the ONLYOFFICE Enterprise app, and click the button to enter the app settings section.
Then open File Manager to access the app's file system and place the license.lic file to the following folder:
/app/data/license.lic
Restart the ONLYOFFICE Enterprise app to pick up the license.
After that your version of ONLYOFFICE Docs Enterprise Edition will become registered and full-featured.