sim not supported issue
i cannot use my sim,i cannot activate it,it says that my sim is not supported by the provider so please fix my phone
That means your phone is locked to a carrier and you are trying to use a SIM from a different carrier.
You need to contact the original carrier and have them unlock the phone.
How to unlock your iPhone for use with a different carrier
https://support.apple.com/en-us/HT201328