Unable to use SIM
I updated my iPhone 7 successfully and it popped up saying you must update your iPhone to use SIM
iPhone 7
Try to optimize the range of the mobile network, see this Apple article:
If you see No Service or Searching on your iPhone or iPad
https://support.apple.com/en-us/HT201415
See also this Apple article: If you can't activate your iPhone
https://support.apple.com/en-us/HT201407