My iphone when I start they said Sim not valid

It may be possible that the SIM card, that is inserted in this phone, is either defective or has not been activated by your cellular voice provider.

The article that you came here from provides you with what you can do to resolve this. If that still doesn't help, I suggest that you first contact your cellular provider, and then, Apple Support directly. To get to the latter, just select the "Get Support" link in the upper right-hand side of this forum's web page.

Then you bought a carrier locked device. Put in a sim from that carrier.

Please read the article that you came here from. It should provide you with how to resolve this.