Trigger NI-5172 via NI-6602

I have a NI-5172 Scope in a NI-1078 Chassis.

The Scope should be triggered by a TTL pulse that goes into a NI-6602, Pin 6 (PFI 5) (also in the NI-1078).

I wrote a control software in C (NI-Scope).
I can trigger the NI-5172 via its Channels but not via an external trigger (niScope_ConfigureTriggerDigital).

I checked all digital channels (VAL_RTSI_0-7, VAL_PFI_0-7), no triggering.

Ho can I rout the trigger signal from the NI-6602 to the NI-5172?
Do I have to map anything in NI-Max?
Can I do it via my software in C (niSync, DAQmax...)?

I played around a lot. I can't find a solution.

Thank you in advance.