SSO Problem: Works remote with IP-Adress but not with FQDN (non HTTP communication)

Question

We are using an application that runs as a service under an Active Directory service profile. With a UI I can log on to the service locally with SSO. If I start the UI remotely and enter the IP address of the service computer as the destination, the SSO login works from there. However, if I enter the FQDN as the destination, the connection will fail. The error message is:

"System.ServiceModel.Security.SecurityNegotiationException: Error in SSPI call, see internal exception. ---> System.Security.Authentication.AuthenticationException: Error in SSPI call, see internal exception. ---> System .ComponentModel.Win32Exception: The target principal name is incorrect"

I tried configuring an SPN, but can't find the correct parameters. The UI uses WCF to communicate with the service. I've found a bunch of information how to configure SPN for MSSQL or HTTP but nothing works.

Environment: Windows Server 2019, Windows 10, .NET-Framework 4.8, Active Directory