I hadn't used my sim for 4 weeks. I changed the sim back yesterday after having it out, and it has been saying Sim 1 Not Provisioned. I've restarted many times. Not sure what to do or what could've happened.
Welcome to the community!
Have you tried to re-position the SIM card? It's also possible that the SIM might have been damaged with repeated removal/insertions. Are you able to try that SIM in a different device? If the SIM doesn't work in a different device, you might need to have it replaced.
If you were using a different SIM card in your phone, have you verified that your phone is using the proper APN? Using a different SIM might have switched APNs. You can verify the APN settings here.
Hope this helps 😀