I’ve checked the APN settings and as far as I can tell they all look correct, but when I put my iD Mobile SIM in the Galaxy S9 (which is running /e/ OS 3.0.4) it won’t connect to the network.
I’ve reset the network settings, and checked the SIM in another phone (which worked). I’ve also tried using the three.co.uk APN, but no luck there either.
Is this an exact match with the published carrier version?
You might report your problem to the carrier and ask for an OTA APN reset. The call handler may treat this as an “unusual request” but may be able to put it in hand if asked “in the right way”.