Unable to connect an ORBI RBS750 satellite to an ORBI67 router

After many attempts, I'm unable to connect an ORBI RBS750 satellite to an ORBI67 router. I've been using the ORBI app in an iPad, and following the steps therein, and the app doesn't discover the new satellite, and after a time the satellite shows a steady purplish red indicator on the bottom of the satellite.

I already have two RBE770 satellites connected to the ORBI67 and they work fine. In googling I confirmed that the RBS750 should work with the ORBI67, but of course google search does not always give correct answers. I've tried resetting the RBS750 the reset appears to work but doesn't help.

I've tried powering off both satellite and router, and restarting both. On reboot the satellite flashes white, and I've tried pressing sync buttons on one or both in repeated attempts. It's possible there's some timing needed in the sequence of steps, and/or duration of hold on sync buttons, but I've tried variations and nothing seems to work.

I'd appreciate advice any relevant information as to how to diagnose and/or fix the problem.

Thanks