Mod Edit (@harrisonhjones): Solution: T-mobile managed to remove the data allowance from the plan while activating the SIM. Swapped cards with my phone and it hooked right up, no problem.
Activated a new third party SIM card on a previously claimed device, got to the point where it attempts to connect to the particle cloud and gets stuck.
I’ve tried fixing the keys per other posts, but no dice. Unclaimed the device in case it was getting confused, didn’t help.
Don’t know what else to do.
Did you follow this: https://docs.particle.io/faq/particle-devices/electron-3rdparty-sims/electron/ ?
Yep.
It’s a t-mobile SIM. Tried with epc.tmobile.com and fast.t-mobile.com. No such luck.
How exactly did you try to do that, and what was the output of those commands?
Does it work if you put the Particle Sim back in?
Got it figured out.
T-mobile managed to remove the data allowance from the plan while activating the SIM. Swapped cards with my phone and it hooked right up, no problem.
Documentation needs better descriptions of the coding used with the LED. If it’s going to be displayed, it ought to have a good description of what it means.
Breathing cyan with red flashes means connected to the cell tower but unable to connect to the cloud (aka no internet connection) which is what is happening for your case. 