Sim800l can't connect to network

Hi everyone, I was using a raspberry pi zero to do connect to a sim800l and I used LM2596 step down transformer to lower the voltage to around 4.3V. I’ve measured it using a multimeter and noticed that the voltage keeps jumping up and down between 4.1-4.3v. The led on sim800l keeps blinking every 1 second and when I use CBAND to change the mode to ALL_BAND it seems to blink every 1 second for 10-12 times and stops for 3-4seconds then repeat. Any idea what is the problem?