Installation of round bike cadence sensor - in the end of crank screw? I got a "LIVALL® P1 Smart Bicycle/Bike Nano Cadence Sensor", round and flat which appears to have a screw in for the end of the crank. However on all the bicycles I see there is the hexagonal screw nut and a black thing around it... just about the size of the threads.

Is this compatible with some way to remove that black spacer or do I need to try to awkwardly zip tie it to the crank somewhere to not rub on anything?

 from Maker's Website
Looking at the video (the English version I linked in the comments), there are several options for installation.  The sensor can act as a replacement for the dust cap found on many cranksets (methods 1 and 2). The dust cap sometime screws in.
This doesn't work if the dust cap and crank bolt are combined (as on Octalink, and similar to what you describe).  I don't think the sensor is designed to replace the crank bolt in that case, but even if it is, I'd be very cautious.  Instead the 3rd option (cable-tied to the inside of the crank arm) is probably the best bet