Wireless Joint

I just activated an AT&T prepaid SIM with the Unlimited Plus Monthly Plan. I activated it on a phone first (Moto E6) and then the modem. It worked just fine on the phone, but every time it's in the LB1120 I get a flashing light, the middle signal bar is lit up and when I go to the modem's GUI, it states SIM Not Installed. I've cleaned and re-inserted the SIM and restarted the modem about 10 times now. I've also re-tried the SIM in the original Moto E6 a second time and also tried in a Google Pixel 3 XL and had no issues with either of those.

Is AT&T blacklisting these devices? Or is this plan simply not compatible with this device?

Could be the slot.. Have you tried a different sim?

Is the sim a nano sim? The LB1120 requires a micro sim, so if you have a nano sim, you need an adapter for it to work in the LB1120.