SIM800l is not Avalible
Try to connect your module with the power supply useing wires as short as are is possible. I was fight with this module for few months and now I know that almost all of issue with it are regarding power supply.
For short test you can connect module directly to LiPo 3,7V.
You have to be sure that your power supplay can handle 2A current. The voltage never can drop below 3,4V.

The power IC and the bypass capacitor should be placed to the module
as close as possible.

SimCom, SIM800_Hardware Design_V1.09, available 27.11.2020