Troubleshooting a _getSSORedirectUrl() must be of the type string, null given Error
Symptom
When clicking Login to Control Panel for a Plesk service, you may encounter the following error message:
Plesk API Response: Plesk_Manager_V163::_getSsoRedirectUrl(): Argument #2 ($username) must be of type string, null given, called in /path/to/whmcs/modules/servers.plesk/lib/Plesk/Manager/Base.php on line 0Cause
The Other product type does not support single sign-on.
Solution
To resolve this issue, change the Product Type setting:
1. Go to Configuration > System Settings > Products/Services.
2. Edit the desired product.
3.For Product Type, select Shared Hosting or Reseller Hosting.
4. Click Save Changes.