I am unfamiliar with universe-1.20.6.jar, can you try with the standard Paper. If it still doesn't work, please provide your startup log.
Startup log
Please follow the steps below:
- Stop server
- Start server
- Wait until your server has fully started and players are able to join
- Go to your server files
- In your default directory, find the `logs` folder
- Download `latest.log`
- Send the log here
This log will help me get a full view of your servers setup, to better help identify the issue.