The code is written in Arduino IDE for STM32F103C8, and is missing the part that would send a custom SMS using Sim800L module whenever the given pin activates.
Additional instructions are commented in the attached code file.
1) Knowledge of Arduino IDE
2) Knowledge of SIM800L module
3) Knowing how to use Arduino IDE with STM32
Hi, I have experience with Arduino Programming, I have good knowledge with SIM800l and know how to use stm32in Arduino ide. I can help you with your required code, let us discuss further over the chat.