Find Plesk License key
To find Plesk serial number on Linux server, run
grep key-number /etc/sw/keys/keys/key* | grep PLSK | awk -F "<|>" '{print $3}
You can also use
plesk bin keyinfo --list
But the plesk_key_id you get is in diff format, plesk themself won’t accept this when you submit a support ticket.
You can also find Plesk License key by logging into Plesk
Plesk > Tools & Settings > About Plesk
On next page you will see