insert.php

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
} 
  $payment_id = $response['payments'][0]['payment_id'];
  $buyer_name = $response['payments'][0]['buyer_name'];
  $buyer_email = $response['payments'][0]['buyer_email'];
  $purpose =  $response['purpose'];
  $payment_status = $response['status'];
  $payment_amount = $response['amount'];

$query = mysqli_query($conn,"INSERT INTO TABLE_NAME (payment_id,buyer_name,buyer_email,purpose,payment_status,payment_amount)
                      VALUES('$payment_id','$buyer_name','$buyer_email','$purpose','$payment_status','$payment_amount')");

if ($query) {
    echo "Data Inserted";
} else {
    echo "Error: " . $sql . "<br>" . mysqli_error($conn);
}

mysqli_close($conn);
?>