Hi Werner,
Correct value for the parameter snc/identity/as should be like "p:<DOMAIN_NAME>\SAPService<SID>"
Also you can follow below steps to check if SNC and SSO are configure correctly or not.
• is SSO working?
To check: execute function module (SE37) create_rfc_reentrance_ticket and confirm that a long alpha-numerical string is returned without any exception.
Example of ticket: AjExMDABAAxTSEFIREVFICAgICACAAMwMDADAAhROTkgICAgIAQADD...... (Length 255 char)
• is SNC active?
To check: execute function module (SE37) SNC_GET_MY_INFO and confirm it is active.
Let us know if you observe any issue in checks?
Regards,
Prithviraj.