Is it possible to use one Plesk license on multiple servers?
According to End-User License Agreement, one Plesk license can be used only on one Plesk installation at a time. You should have a valid license key for each server on which Plesk is installed.
If you have multiple license keys for the software, you may make and use as many copies of the software as the number of license keys you have.
For details, please refer to the End User License Agreement: https://www.plesk.com/terms-and-conditions/