- Plesk Onyx for Linux
- Plesk Onyx for Windows
- The option Forbid customers to change the name of their main domain set in Tools & Settings > Server settings
- Reseller also unable to change the customer's main domain
In the description of the option should be written that reseller is also unable to change the customer's main domain.
This is bug #PPP-43833 which will be fixed in the next Plesk updates.
Until the bug is fixed, there is no available workaround.