How to communicate with sim800c using Raspberry pi 3 in c++

My end goal is to try and send some simple data that's stored on my Raspberry pi 3 to an external server/website using a sim800c from a c++ program. I believe the easiest way to do this is to issue "AT commands" to the sim/modem however I'm struggling to do this. I can't figure out how I'm actually suppose to issue AT commands or how I can check if they're working. For testing purposes I've written some code which should send a text message to a phone number once I've gotten this working it should be fairly straight forward to figure out the AT commands to communicate with a server.

Below is an image of how I've wired everything up which I'm fairly confident is correct.

https://i.sstatic.net/ssSQq.jpg

Below is the basic c++ code that I've written using various guides, it compiles and runs in terminal however I don't get any response from the AT commands and more importantly as far as I can tell their not actually being executed. I've tried changing the fake number to my personal one but it didn't make a difference.

#include <stdio.h>
#include <string.h>
#include <wiringPi.h>
#include <wiringSerial.h>

int main ()
{  

    int connection;

    printf("Opening connection \n");
    connection = serialOpen("/dev/ttyAMA0", 9600);
    delay(1000);
    printf("Connection:  %d\n", connection);
    printf("\n");

    //Set gsm to text mode
    serialPuts(connection,"AT+CMGF \r\n");
    delay(1000);

    //Number that the message should be sent to
    serialPuts(connection,"AT+CMGS=\"12345678900\"\r\n");
    delay(1000);

    //The message
    serialPuts(connection,"Hello World");
    delay(1000);

    //Print ctrl+x
    serialPuts(connection,"\x1A");

    delay(1000);

    printf("Done \n");

    return 0 ;
}

As far as I can tell there are 3 likely reasons why it's not working;

A possible config/settings issue with the pi
I've wired it up incorrectly
The sim/module isn't working

I'm just not sure how to go about testing/finding what is causing the issue. If I could get my code to output the response of the AT commands after doing "serialPuts" that might help me figure out whats going on but I haven't made much luck doing that. Alternatively If anyone has an idea why the commands don't appear to be working or can provide me some ways to debug/test them that would be great.

Solution

The issue turned out just to be a simple wiring mistake.

I had wired the txd pin of the sim module to the txd pin on the raspberry pie as I was under the impression you just needed to match the pins however I didn't think/realize that the txd pin needed to go to the rxd pin instead. Changing these around allowed me to see the commands & responses being returned from the module. To actually get the gprs working I also needed to temporarily set the pwr pin to low then high.