Access Project Online from Project desktop client

Hallo, I need your help please.

I have Project online desktop client and can't connect to the Project Web App. Error says "Project was unable to establish a connection with [Project Server URL]. This could be caused by a loss of network connectivity or inadequate permissions to connect to Project Web App."

The URL name is defined in Project online desktop client as https://xxxxxxx.sharepoint.com/sites/PM.MCO

I have been granted P5 license and defined in the security groups of Project managers and administrators