New Moto G 4 th gen arrived with SIM card installed, yet phone says no sim installed, will not activate
I had the same issue a week ago. I removed the SIM card and reinserted it and it’s been fine since.
If reinserting the SIM doesn’t fix your issue, then open a support ticket at the bottom of the help page. Use the chat line if available for faster service. Republic Help
I agree with @steve.e. Powering down your Moto G4, then reseating the SIM card is the logical first step. Some guidance from Motorola here: Insert or remove the SIM card - Moto G Plus (4th Gen.).
I also experienced this with a G4+ I activated last Saturday. Removing and replacing fixed it. I wonder why this is happening.