I am learning how to make android app.
I am getting “Uncaught mysqli_sql_exception: You have an error in your SQL syntax;” error. since I am new to php and database I am not able to reslove the issue. I hope you guys will help me.
I am providing everystuff to seek better help.

Mysql database: Database Image

The error: Error in postman

I am getting error in this part of code:

if($request->{'action'} == 'ADD_NEWS'){
        $isValidRequest = true;

        $headline = $request -> {'headline'};
        $description = $request -> {'description'};
        $userId = $request -> {'userId'};

        $query = "INSERT INTO news('headline','description','user_id') VALUES ('".$headline."','".$description."','".$userId."')";
        $result = mysqli_query($connection,$query);
        if($result){
            $response['newsId'] = mysqli_insert_id($connection);
            $response['status'] = true; 
            $response['responseCode'] = 0; //News Added Successfully
            $response['message'] = "News Added Successfully";               
        }else{
            $response['status'] = false; 
            $response['responseCode'] = 102; //News not added
            $response['message'] = "News Not Added";
        }

The line i am getting error in is: $result = mysqli_query($connection,$query);

The whole code:

<?php

include 'config/db_config.php';

$data = file_get_contents("php://input");
$request = json_decode($data);
$response = array();
$isValidRequest = false;

//{"action":"REGISTER_USER","userName":"Mr. Amir"}
//REGISTER_USER
//ADD_NEWS
//GET_NEWS
//UPDATE_NEWS
//DELETE_NEWS

if(isset($request->{'action'})){
    if($request->{'action'} == 'REGISTER_USER'){
        $isValidRequest = true;
        $userName = $request -> {'userName'};

        $query = "INSERT INTO user(name) values('".$userName."')";
        $result = mysqli_query($connection,$query);
        if($result){
            $response['userId'] = mysqli_insert_id($connection);
            $response['status'] = true; 
            $response['responseCode'] = 0; //User Registered Successfully
            $response['message'] = "User Registered Successfully";              
        }else{
            $response['status'] = false; 
            $response['responseCode'] = 102; //User Registered Failed
            $response['message'] = "User Registered Failed";                
        }
    }

    if($request->{'action'} == 'ADD_NEWS'){
        $isValidRequest = true;

        $headline = $request -> {'headline'};
        $description = $request -> {'description'};
        $userId = $request -> {'userId'};

        $query = "INSERT INTO news('headline','description','user_id') VALUES ('".$headline."','".$description."','".$userId."')";
        $result = mysqli_query($connection,$query);
        if($result){
            $response['newsId'] = mysqli_insert_id($connection);
            $response['status'] = true; 
            $response['responseCode'] = 0; //News Added Successfully
            $response['message'] = "News Added Successfully";               
        }else{
            $response['status'] = false; 
            $response['responseCode'] = 102; //News not added
            $response['message'] = "News Not Added";
        }
    }

    if($request->{'action'} == 'GET_NEWS'){
        $isValidRequest = true;
    }

    if($request->{'action'} == 'UPDATE_NEWS'){
        $isValidRequest = true;
    }

    if($request->{'action'} == 'DELETE_NEWS'){
        $isValidRequest = true;
    }

    if(!$isValidRequest){
        $response['status'] = false; 
        $response['responseCode'] = 100; //Invalid request action
        $response['message'] = "Invalid request action";
    }
}else{
    $response['status'] = false; 
    $response['responseCode'] = 100; //Request action not defined
    $response['message'] = "Request action not defined";
}

echo json_encode($response);

?>