Sim not supposed issue.

What is your question? The message itself explains the situation, and paths forward.

Your phone is locked to a specific carrier - many carriers sell iPhones on a discounted basis, on the expectation of making up the difference in an ongoing contract or usage fees.

To use the phone on a different carrier, the original carrier needs to 'unlock' the phone - this releases the carrier lock and enables other carriers' SIMs to be used.

So, assuming you know the original carrier, you need to contact them to get them to unlock the phone, or get a SIM from that carrier so the lock doesn't matter.