Hi,
when Allocatus Server checks the availability of Project Server or if it syncs tasks for a particular users it tries to identify the user by his/her Windows account. If you are using classic-mode authentication with Windows all user logon accounts must have the notation Domain\UserName. If your are using claims-based authentication with Windows all user logon account need to have the notation i:0#.w|Domain\UserName.
You can change the user logon account for Project Server users if you go to Project Web App/Server Settings/Manage Users. You only need to update the user accounts for users that are synchronized by Allocatus and for the service account used by Allocatus Server to access Project Server.
If you are using-claims based authentication you need to have Allocatus Server 3.7.4 or higher and you need to set the tag ClaimsBasedAuthenticationEnabled in config.xml to true. Please note that you cannot use forms-based authentication (fba). It's possible to run FBA on a separate web application, how ever the web application running the PWA Url configured in Allocatus Server settings needs to be set to Windows authentication only.
Allocatus Admin