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 0

Cause

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.

Change the Product Type setting

4. Click Save Changes.