From the above link, it is the code I used for home automation using sim800L module, arduino and relay.

I tried sending message and calling to switch on the relay, but neither worked.
I'm confused and don't know where the problem could be from.

Please, I need your help.

@bargain, your topic has been moved to a more suitable location on the forum. Installation and Troubleshooting is not for problems with (nor for advise on) your project :wink: See About the Installation & Troubleshooting category.

Bad wiring? Incorrect wiring? Maybe start with a simple example for the SIM800?

Please post your code here in code tags.