SXT LTE +CME Error: 100 using EE

I’m in the UK and trying to set up SXT LTE using an EE sim. I have tried an O2 sim and it kicks straight in no problem despite the O2 signal not being so strong. When I insert either of two EE sims I get an error +CME Error: 100. Everthing is at default - I have not added any APN, as was advised it should just work (as the O2 one did). Any help or advice appreciated.

Any help greatly appreciated. I have now tested in two locations and it is obviously a sim specific problem. I’ve checked with EE who advise there’s no locks on SIM or any other reason it shouldn’t work.

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AS an update to anyone reading this I resolved the problem. It seems EE is alone in requiring an APN setup - I used the following (think its just username and password needed which I put in as CHAPS):
Name: EE internet
APN: everywhere
Username: eesecure
Password: secure