Frage VFD setup with M700 + UCCNC

Hi,
I'm trying to setting up a HF spindle + AT1 inverter on my M700 machine.
Either I get PWM + 5V START SIGNAL direclty from the SUB-D (Case1)
Or I get a 0-10V analog speed signal from the PWM converter cable ( shop.stepcraft-systems.com/PWM-Converter-Set ) but no START SIGNAL

In both case I'm stuck :
- My VFD doesn't read PWD
- I need a kind of relay to connect VFD ground to START pin. The 5V signal doesn't do the trick

So at the moment I'm using the spindle manually.

Is there any advice to read ?