7i95T spindle control via Modbus RS485 and SPINX1A

Yes its SPINX1A, the 10.75 voltage comes from the VFD, I have a delta VFD,and I have wired this way:
+10v -> spinx SP+
ACM -> spinx SP-
AVI -> spinx SPV

Between SP+ and SP-, I measure 10.75

If I reduce the RPM at 100 rpm, the pwmgen value is correct, but the voltage between SPV and SP- is still 5.45

That sounds like either the SPINX1A is damaged or perhaps the wiring is incorrect.

I would verify SPINX1 operation by running SPV+ and SPV- from 5V and GND from the
7I95 to verify its operation independent of the VFD

Also SPINX1A PWM frequency should be 20 KHz (though this should just affect ripple)

The problem was that I had pwmgen.00.offset-mode set to 1
Once I set this to zero, now the voltage is correct.
I've set the pwm_frequency to 5000 initially, then after your last comment, I increased it to 20000, but didn't noticed any difference.
Not sure what this does exactly and why would it matter if its higher.

Thanks for your help so far!

The SPINX1A has a 2 pole ~ 100 Hz RC filter to average the PWM signal.

Too low a PWM frequency will let noticeable ripple through the filter.
Too high a PWM frequency will result in poor linearity, (as the switcing
time of the OPTO becomes a significant part of the cycle time)

For the SPINX1A, 20 KHz is about the optimum compromise between ripple and linearity.