How To Resolve The Sim/usim Card Has Not Been Detected Or Is Invalid Error
That is a common problem with devices that uses SIM card. It usually happens when the SIM card is not inserted properly or the contact surface needs a little cleaning. If your SIM card is new and you just bought it, try removing it from the SIM slot and then insert it back again. See if this works.
But if the SIM card is slightly old, one possible reason is a dirty contact surface. I usually encounter it on my previous SIM cards and cleaning is the best remedy. Turn off your phone then remove the SIM card. Get a pencil eraser then rub it on the SIM card’s contact surface, the side that has direct contact to the pins on the SIM slot.
After this, wipe the surface clean with a clean cloth then insert it back to the phone. Turn on your phone and see if it works.