Can Plesk resellers and customers use REST API?
This feature is yet to be implemented in Plesk. At the moment, REST API is only available for the Plesk Administrator account.
If you would like to see this feature in Plesk, please vote for it on Plesk UserVoice:
As a workaround, resellers can use XML API: Resellers have access to a limited number of operations within each particular version of XML API. When using a reseller account, a strict requirement is that the option Ability to use XML API is selected in the reseller subscription properties, on the Permissions tab.
For more details, refer to Plesk documentation: