I have recently set up my new iPhone and I put my SIM card in and a message comes up saying SIM not supported. The phone was brand new so should not be locked. My SIM is Virgin so uses EE signal so I don't know why it isn't working.
iPhone XR
The phone you bought is carrier locked. apparently to a carrier other than the one you're using.
Where did you buy it? The only place you can purchase a new, unlocked iPhone is directly from Apple.
Only the carrier that has the lock can remove it.
If you paid for it using a credit card I would dispute the purchase.
I bought it off Ebay. How do I unlock it?
You contact the carrier it is locked to and find out if you qualify to get it unlocked. See here: https://support.apple.com/en-us/HT201328
SIM card not working
