Android, PHP - Passing inputted variable from Android to PHP $_SESSION and use the $_SESSION variable to get data

I'm really having a hard time dealing with "fetch user-specific data". Thing is I planned to log into my Android Application and when I go to a different activity (ProfileActivity), I can see my own profile data (in this case, "Full Name" and "Job") directly from PHP and MySQL Database. That was what I initially wanted. I have my own SharedPreference and it works perfectly BUT somehow it only stores my Username and Full Name (because I have RegisterActivity) and not my "Job". I've tried reading several solutions like storing in SQLite or tokens but mostly I can't get to that point and I can't get it to work.

But then I thought of using the $_SESSION in PHP. What's in my way of thinking was: First, I start my Android App and input my credential to login (Username and Password); Then, the inputted variable (Username) is stored and processed in PHP $_SESSION (loginget.php); After that, I planned to use that $_SESSION to be used to another PHP files (e.g. c.php) and display it in either Android textview or recyclerview for future needs.;

That was I initially wanted it to work, but couldn't.

I have this PHP login file that accept username and password loginget.php.

<?php
$response = array();
include 'koneksi.php';
include 'functions.php';
session_start();
//Get the input request parameters
$inputJSON = file_get_contents('php://input');
$input = json_decode($inputJSON, TRUE); //JSON decode convert JSON into array. (JSON is from android input, array  is for php)

//Check for Mandatory parameters
if(isset($input['username']) && isset($input['password'])){
    $username = $input['username'];
    $password = $input['password'];
    $query    = "SELECT full_name, job, password_hash, salt FROM member WHERE username = ? ";

    if($stmt = $con->prepare($query)){
        $stmt->bind_param("s",$username);
        $stmt->execute();
        $stmt->bind_result($fullName,$job,$passwordHashDB,$salt);
        if($stmt->fetch()){
            //Validate the password
            if(password_verify(concatPasswordWithSalt($password,$salt),$passwordHashDB)){
                $response["status"] = 0;
                $response["message"] = "Login successful";
                $response["full_name"] = $fullName;
                $response["job"] = $job;

            }
            else{
                $response["status"] = 1;
                $response["message"] = "Invalid username and password combination";
            }
        }
        else{
            $response["status"] = 1;
            $response["message"] = "Invalid username and password combination";
        }

        $stmt->close();
    }
}
else{
    $response["status"] = 2;
    $response["message"] = "Missing mandatory parameters";
}
$_SESSION['yes_msg'] = $response["full_name"];
echo json_encode($response);

?>

And this c.php used to fetch the Profile Data ("Full Name" and "Job") from MySQL Database:

<?php

session_start();

$SESSION = $_SESSION['yes_msg'];
include 'koneksi.php';
include 'functions.php';
//if everything is fine then create an array for storing the data 

$resp = array(); 

$sql = "SELECT full_name,job FROM member WHERE username = '$SESSION'";

//creating an statment with the query
$stmt = $con->prepare($sql);

//executing that statment
$stmt->execute();

//binding results for that statment 
$stmt->bind_result($full_name,$job);

//looping through all the records
while($stmt->fetch()){

    //pushing fetched data in an array 
    $temp = [
        //'user_id'=>$user_id,
        //'username'=>$username,
        'full_name'=>$full_name,
        'job'=>$job
    ];

    //pushing the array inside the hero array 
    array_push($resp, $temp);
}

//displaying the data in json format 
echo json_encode($resp);
?>

It looked like I placed the $_SESSION function on loginget.php at the wrong place and can't get it to work. In c.php, the GET function worked fine when I tested with static variable and it shows on the Android Activity.

But when I tried to connect it with loginget.php, the data is not showing or fetched, but there are no errors as well.

I really appreciated hint or answer, for this is probably beginner's mistake as I am a beginner as well and this is my first time writing and asking a question.