For future viewers of this thread, the API key is the same as the MAC address. You can usually find this on your router config where it shows device info. The MAC is also shown in the serial output when you connect a burner device (or FTDI cable as mentioned above.

My problem was the device was stuck and needed reflashing. Once I did that it worked perfectly using the 12-digit MAC as the API key.

You may safely ignore the 8 digit "API Key" that is shown in M5burner or the command line, this was a red herring.

@felmue you are a god. I didn't want to order a $15 burning tool for my $5 m5stamp so I've been using a cheapo FTDI adapter. Connecting GPIO0 to GND worked like a charm.

When I boot in UIFlow mode this is how the serial output looks. But M5burner and esptool won't work at all...

@ajb2k3

I hooked up a FTDI adapter and am seeing these errors in the serial output. Did I get a bad board?

14:41:58.735 -> Start factory test
14:41:58.735 -> Start IO TEST
14:41:59.066 -> 18 >>>> 1
14:41:59.111 -> error HIGH-->>>OUT:26  IN:18
14:41:59.738 -> 18 >>>> 0
14:41:59.770 -> 21 >>>> 0
14:41:59.815 -> error HIGH-->>>OUT:19  IN:21
14:42:00.434 -> 18 >>>> 0
14:42:00.473 -> 21 >>>> 0

I also noticed every other device in UIFlow uses an 8 character API Key (MAC). The m5stamp is the only one that requires 12. Could this be a bug or unfinished configuration in the app?

As a last resort I tried the actual real MAC address of the device that I got from my router. That failed too, although I can see the device is definitely on the local network.

The docs suggest that the WiFi AP name doubles as your API key. But it's only 8 characters, UIFlow wants 12 characters:

I don't have the little USB adapter so was hoping to just fiddle around in UIflow to get started. Anyone know the secret to finding the API key on these? Did something change about the way it is configured?

I think I probably have a defective unit. I have tried with only a single tab open, latest version of Google Chrome, tried it incognito mode also just to be sure some extension wasn't getting in the way. Despite all efforts it never connects to UIFlow. I know it's on the network because my router is showing it connected and sending/receiving some packets.

I will probably stick with devices that have USB-C on them, this is way too much hassle and I don't want to have to rig up a programmer just to toy around with a prototyping device. Oh well, at least I'm only out $5.

Ok so the green pulsing light means "Normal, connected, ready for UIFlow"?

As you can see I'm not doing anything especially exotic or weird here:

How it looks when I click the Run button in UIFlow:

How it looks when I click the Download button and let the app run on its own: