The "TEST CONNECTION" fails with the "incorrect username and password" error message for an NSX cloud account that is part of the VCF stack and has the "System Managed Credentials" checkbox activated.
Error - Failed to establish connection to NSX manager due to an incorrect username or password
The same could also happen for the vCenter cloud account.
VCF Operations 9.0 and later
There could be multiple causes for this issue. Following are the most common ones:
In the Administration → Integrations page of VCF Operations, expand the VCF Instance and navigate to the domain.
On the domain page, click the NSX tab. Next to 'System managed credentials', click 'Rotate'.
The existing service account gets deleted and a new service account is created.
The same resolution applies for vCenter cloud account as well.