Another instance of Certbot is already running (Kill Certbot)
To fix this error, you need to wait until the first instance of Certbot has completed its operation, or you can check if there are any active Certbot processes and kill them.
Here's how you can check and kill active Certbot processes
Run the following command to see the list of active processes:
ps -ef | grep certbot
Find the process ID (PID) of the Certbot process that is running. The PID will be listed in the first column of the output.
Run the following command to kill the Certbot process, using the PID that you found in the previous step:
sudo kill [PID]
Once you've killed the active Certbot process, you should be able to run the Certbot command again without encountering the error "Another instance of Certbot is already running."
Note: Killing an active Certbot process may interrupt the operation of your SSL/TLS certificates, so be careful when using the kill command and only use it if you're sure that it's necessary.