LED Shim error

Just got the LED shim, and can’t get it to do its magic when I call show():

Traceback (most recent call last):
File “shim.py”, line 22, in
File “/usr/lib/python2.7/dist-packages/ledshim/is31fl3731.py”, line 243, in show
File “/usr/lib/python2.7/dist-packages/ledshim/is31fl3731.py”, line 93, in setup
raise e
IOError: [Errno 121] Remote I/O error

What’s going on here? I2C is enabled. physical connections are good.

IO error usually means the connections aren’t good. How do you have it connected? Try tilting it a little bit to force a good connection and see what happens. Or plug a female header in on top of it to hold it down tightly, just for testing.
They went to a lot of work to make it work by just plugging it in on top of your GPIO header without having to solder it but IMHO, it can still be a bit finicky. I have two LED Shims, I soldered headers on mine. Its more so I could remote mount them via jumper wires though. No issues here doing it that way though.

which pins are the critical ones, and for that matter, which way is it supposed to go on? Pin1 isn’t indicated on the shim.

Pinout is here, meant to post this earlier.

It looks like the end with the little copper dot is the pin 1 end.

OK, It’s working on my Pi 3B, but not on the Pi 0W

Mine are wired up to Pi A+'s (A+ not a 3A+). I “think” I test ran my first one on a Zero and no header on the LED Shim? The model of Pi shouldn’t matter, they all have the same GPIO pinout, all the 40 pin ones anyway.
Best guess is one or more pins isn’t making a good contact.