My Jamaican SIM isn’t working on my iPhone

You purchased a phone that is locked to a carrier. You will need to contact that carrier and ask them to unlock it before you can use your new carrier.

How to unlock your iPhone for use with a different carrier - Apple Support

If the phone is locked and you can't get into it, that is a completely different issue then what you said in your first post.

So why don't you explain in detail what you are having issues with.