Hello,
My M7E does not have a stable connection to my Pi 4 Model B using USB c to a cable. When looking at connections to USB bus on the Pi the serial convertor will briefly appear and disappear. The power LED on the M7E is blinking. I suspect there might be an issue with the RFID board? The Pi should be able to supply enough power via USB HUB. I will do more troubleshooting tomorrow
Try swapping cables to one that you are certain has working data lines. Are you using the blue or black usb ports? Try a blue one
Your Pi is not providing enough power, the blinking LED is evidence of that. Consider adding an external power supply to the M7E.
I will try. The Pi 4 should supply up to 1.0A @5v total thru USB which should power the M7E (I think), but maybe i’m a noob and am missing some understanding.
I tried both 2.0 and 3.0 ports. Pi4 docs state USB can supply 1.2A thru USB (raspberry-pi universal-serial-bus-usb) and M7E docs state required power can be up to 700mA (3.6W @ 5V), which should be within the capabilities of the Pi4. Is my understanding okay or do you think im missing something? Im using a 30W 5v power supply, but I will doublecheck @TS-Russell thank you
No, it can only supply a combined 1.2A…I think it’s 500mA max per individual usb port (which I forgot earlier!)
YellowDog is right, go ahead and power it externally
thank you @TS-Russell and @YellowDog . I got it to work!
Short answer: I soldered the 0-ohm resistor incorrectly.
Long answer: I tried to troubleshoot using a windows machine with Jadak software. It detected the M7E but I could not scan anything. I went to check continuity between the external trace to see if there was any power getting to the external antenna when I realized the 0 ohm link was soldered incorrectly onto the wrong pad 
after re-soldering the link it works as expected on both a windows machine and the Pi. learning lesson.
That’s awesome!