I got sent a phone and while transferring my data over as well as my SIM card it came up that my sim was not supported and that it was not a system issue and to either get a new sim from a different issuer or request to have Thé phone unlocked
[Re-Titled by Moderator]
Original Title: Sim not supported
iPhone 11, iOS 18
That usually means the phone is locked to a carrier and ONLY the carrier the phone is locked to can unlock it. Apple cannot unlock a carrier locked iPhone. You got "sent an iPhone?" From whom did you get the iPhone? You need to contact them to determine the carrier the phone is locked to. Then you'll need to contact the carrier and see if the phone qualifies to be unlocked, which will likely require paying off any unpaid balance due on the phone contract.
I'd return the phone to whoever "sent" it to you.
Read this --> The All Too Common SAD Reality of Buying … - Apple Community
This sounds like the iPhone you were sent is carrier locked, and the SIM you are trying to insert is one not compatible with their network. You would need to contact that carrier and ask them about the unlocking requirements. If you paid money for this iPhone I would suggest you return it because if you don't switch to a SIM on their network, unlikely you'll be able to ever use a cellular connection on it and sacrifice many primary features of iPhone such as Phone.
How to unlock your iPhone for use with a different carrier - Apple Support
That phone is carrier locked. Only the carrier it is locked to can unlock it for use on other networks.
Who sent you the phone?
SIM card not supported on new iPhone
