Wireless Joint

I use unlimitedtogo blue and had an SIM issue, to which they sent me a new SIM. I don't recall how I activated the last SIM because it was a long time ago. I powered off my modem, plugged in the new SIM, powered back on and am getting:

LTE CA state: NOT REGISTERED
EMM state: Deregistered
RRC state: RRC Releasing
IMS reg state: Not Srv

Does anyone know how to register the SIM so I can use it in my modem?
Should I trim the sim down and try it in an old phone?

Is your modem the device registered to the SIM account? If so you should be able to just plug it in. If not, you probably need to drop it in the original device and get that working first, then move the working proven SIM back to the modem.