The script below is based on one one which runs successfully, however this one seems to crash after executing the query. I can’t understand why this one doesn’t work. All tables and column names have been checked!

<?php
include 'connection.php';

print("startedn");

$customerusername = $_GET["username"];
$customerpassword = $_GET["password"];
$customername = $_GET["name"];
$companyname = $_GET["companyname"];
$companydescription = $_GET["description"];
$companyemail = $_GET["email"];
$companyphone = $_GET["phone"];

print("set up connectionn");

// Create connection
$conn = new mysqli($host_name, $user_name, $password, $database);
// Check connection
if ($conn->connect_error) {
  die("Connection failed: " . $conn->connect_error);
} 

print("queryn");
$sql = "INSERT INTO Customer (user_name, pass_word, fullname) VALUES ('" . $customerusername . "','" . $customerpassword . "','" . $customername . "');
INSERT INTO Vendor (company_name, description, email, phone, customer_id) VALUES ('" . $companyname . "','" . $companydescription . "','" . $companyemail . "','" . $companyphone . "', LAST_INSERT_ID());
SELECT * FROM Customer WHERE user_name = '" . $customerusername . "'";

print($sql."n");
$conn->multi_query($sql);
print("query executed");

do {
      /* store the result set in PHP */
      if ($result = $conn->store_result()) {
          while ($row = $result->fetch_row()) {
            print_r($row . "n");
            $completeResults[] = $row;
          }
      }
        else
        {
          print("no results returned but no crash");
        }
  
      /* print divider */
      if ($conn->more_results()) {
          
      }
    } while ($conn->next_result());


$conn->close();
?>