Update error1 when roaming
My daughter has just had this issue. Looking back I see a cluster of posts in May/June on the same issue.
Pure speculation on my part, and I’m no expert, but my suspicion is that her home carrier has just sent out an over-the-air carrier settings update, which fails because she’s not on her home carrier network. It should fix itself when she gets home. I think a short-term fix is to turn off 3/4G.
Hope this helps someone else.
MacBook Air (2018 or later)