iPhone 5 saying SIM not supported
Trying to put my SIM card from iPhone 8 into my iPhone
5 and it says SIM but supported
iPhone 8, iOS 16
That means your iPhone 5 is locked to a carrier different than the carrier that the SIM is from. You need to contact the carrier the phone is locked to and ask them if they will unlock it.
How to unlock your iPhone for use with a different carrier - Apple Support