SIM card not working after factory reset

This is network lock.1st check this iphone

Network sim.First of all, you have to find out which network company the iPhone belongs to. After that, you have to pay for it and get it unlocked.Have you not paid money to that institution?

What is your country?.

Please send this error English.

I would guess that your phone is carrier locked and you need a sim card from that carrier or ask them to unlock your phone.