Plesk Migrator failed to synchronize Subscription with Plan: PHP handler is not allowed in the site isolation settings

Symptoms

• Plesk migration fails:

  PLESK_ERROR: ‘Failed to synchronize subscription with plan
  Migration tools tried to perform operation in 3 attempts: Plesk error [1023]: php_handler_id – Description: The PHP handler is not allowed in the site isolation settings. The default PHP handler will be used.. Requested: cgi-5.6. Allowed: fastcgi-5’

• Subscription syncing fails: 

  PLESK_INFO: Syncing the subscription with its service plan failed because some of the services or resources defined in the plan cannot be actually provisioned with the subscription. Available value indicates the actual state of a resource or a service in the system. Clicking OK will initiate setting the subscription values according to the available values.

Cause

Required handler is not enabled in Tools & Settings > PHP Settings .

Resolution

1. Log in to Plesk
2. Enable the handler mentioned in the error message at Tools & Settings > PHP Settings.
3. Sync the subscription content