Pass array object to API and save to Database

Question

I’m using Ionic 3 and I want to save the data of an object in the database. In the API is running the query and saving null in the database, I imagine the way I am sending the object is wrong. Follow my code:

finaliza(obj){    
    this.pedido.push(this.prod);

      let headers = new Headers();

      headers.append('Content Type', 'application/json');

      let options = new RequestOptions({headers: headers});

      this.service.postData().subscribe(
        data =>obj=data,
        err =>console.log(err)
      );
    }

In the preview:

import { Injectable } from '@angular/core';
import { Http } from '@angular/http';
import 'rxjs/add/operator/map';

@Injectable()
export class ProdutosProvider {

api:string='http://mywebsite.com/';

  constructor(public http: Http) {
    console.log('Hello ProdutosProvider Provider');
  }
  
  getData(){
    return this.http.get(this.api +'app-produtos.php').map(res=> res.json())
  }

  postData(){
    return this.http.get(this.api +'app-pedidos.php').map(res=> res.json())
  }


}

This object is coming from the normal database and in the API for insertion I am using the following code:

<?php
header("Access-Control-Allow-Origin: *");
header('Content-Type: text/html; charset=utf-8');
header("Access-Control-Allow-Headers: Origin, X-Requested-With, Content-Type, Accept");


$dns = "mysql:host=localhost;dbname=mydb";
$user = "myuser";
$pass = "mypass";

try {
        $data = file_get_contents("php://input");
        $objData = json_decode($data);
       
        $id = $objData->id;
        $name = $objData->name;
        $img = $objData->img;
        
       
        // LIMPA OS DADOS
        $id = stripslashes($id);
        $name = stripslashes($name);
        $img = stripslashes($img);
        
        $id = trim($id);
        $name = trim($name);
        $img = trim($img);        
        

    $con = new PDO($dns, $user, $pass);
    if(!$con){
        echo "Não foi possivel conectar com Banco de Dados!";
    }
    
        $conn = mysqli_connect('localhost','myuser','mypass','mydb');
        $sql1 = "INSERT into pedidos_app (id,id_prod,name,img) values (null,'{$id}','{$name}','{$img}')";
        $qr1=mysqli_query($conn,$sql1);      
    
        
} catch (Exception $e) {
    echo "Erro: ". $e->getMessage();
};