SIM800C not registering to network

Hello,
We have designed a sim800C custom module . The sim 800C IC has a direct supply of 4V 2A using a programmable TEK power supply. The sim 800C IC is powering up and it also responds to AT commands.
But it is not detecting my SIM card . I tried to connect to a network manually using AT+COPS =1.0.“IDEA” but it says wrong sim or sim not inserted.
I also tried AT+CPIN? but it again gives me the same error.
I have also tried AT+CFUN=1
I also noticed that the module catches the signal initially for a moment and immediately releases it.
please help!!!

Hi…
Facing the same issue…! error is CME ERROR: 15 SIM wrong for command AT+CPIN? & CME ERROR: 10 SIM not inserted for commands required to build TCP Connections. Please somebody suggest the solution for this issue. My trackers are getting lost in between the journey…

Upload a picture of your setup. Even you have connected 4V 2A, the track/wire length and thickness also plays a role.