AdministratorJanuary 25, 2021 at 7:56 am
1) What kind of SIM800L are you using? There are some with carrier boards and some plane boards.
2) What is the power supply for the SIM800L? It needs special voltage and a lot of current!
3) It is always better to use pins that have unique communication functions. Like the UART2 on the X2. Pins that are used as inputs are additionally protected by 1k serial resistors.