There are 3 variants of LG K20 which are K20, K20 v & K20 Plus. Out of this K20 & K20 Plus are GSM phones whereas K20 v belongs to Verizon and its a CDMA + GSM Phone.
K20 is from AT&T and K20 Plus belongs to MetroPCS / T-Mobile. After knowing the K20 variants it would be easier to troubleshoot SIM card related issues on your K20 Phone.
There are various possibilities for a SIM card failure on your K20 / K20 Plus. First of all, we’re going to re-install the sim card and later on, we’re going to follow the troubleshooting steps –
LG K20 Sim Card Installation – The Basic troubleshooting step
Lift your LG K20 / K20 Plus back cover using the groove as shown above.
Insert your SIM card in the lower slot. The upper slot is for the micro SD card.
Make sure you insert a Nano-SIM in the SIM card slot.
Now reboot your phone and check whether the SIM is working or not.
If it’s still not working then based on the error you’re getting we’re going to resolve the SIM card related issue using the below troubleshooting steps –