Why do I keep getting 405 error when submitting a form to mysql database

I’m trying to submit a form into mysql database but every time I click submit on the webpage I’m getting the HHTP ERROR 405 Method not allowed. I’ve searched but I still haven’t found a solution, can anyone help? Here is my code below.

Here is the requests.html page

form action="conn.php" method="POST">

                <label for="category" id="fname">What type of request are you making?</label>
                <select id="category" name="category" required>
                  <option value="software">Software Update</option>
                  <option value="hardware">Hardware </option>
                  <option value="application">Application</option>
                  <option value="security">Security</option>
                 
                </select>

              <label for="fname" id="fname" >Full Name</label>
              <input type="text" id="fname" name="name" placeholder="Your name.." required>
          
              <label for="fname" id="fname">Summary</label>
              <input type="text" id="fname" name="summary" placeholder="Brief summary..." required>

              <label for="lname">Description</label>
              <input type="text" id="lname" name="description" placeholder="">

              <label for="fname" id="fname">Impact on server or application</label>
              <select id="category" name="server_category" required>
                <option value="sql">MySQL</option>
                <option value="web">EA Webserver </option>
                <option value="server">Oracle Server</option>
              </select>

              <label for="fname" id="fname">Impact on Department</label>
              <select id="category" name="department_category" required>
                <option value="assurance">ICT ASSURANCE SERVICE</option>
                <option value="support">ICT Support Service </option>
                <option value="network">ICT Network and infastructure</option>
              </select>

              <label for="fname">Risk</label>
              <select id="category" name="risk_category">
                <option value="high">High</option>
                <option value="moderate">Moderate</option>
                <option value="low">Low</option>
              </select>

              <!--<label for="fname">Change Start date</label>
              <input type="date" id="date" name="start_date">
              
              <label for="fname">Change Completion date</label>
              <input type="date" id="date" name="end_date">
              -->
              
          
             
            
              <input type="submit" value="Submit">
            </form>

And here is the conn.php code

<?php

$name = $_POST['name'];
$summary = $_POST['summary'];
$description = $_POST['description'];
$server = $_POST['server_category'];
$department = $_POST['department_category'];
$risk = $_POST['risk_category'];
$start = $_POST['start_date'];
$end = $_POST['end_date'];

if(!empty($name) || !empty($summary) || !empty($description) || !empty($server) || !empty($department) || !empty($risk)){


$passw = "dog1234";
   
$username = "root";

$db = "test";

$host = "localhost";

$conn = new mysqli($host, $username, $passw, $db);

if(mysqli_connect_error()){
    die('Connection error ('. mysqli_connect_errno().')'. mysqli_connect_error());
} else{
    $INSERT = "INSERT INTO request_change (employee_name, summary, req_description, req_server, department, risk) 
    VALUES (?, ?, ?, ?, ?, ?)";

    $stmt = $conn->prepare($INSERT);
    $stmt->bind_param("ssssss", $name, $summary, $description, $server, $department, $risk);
    $stmt->execute();
    echo "new record inserted";
}

$stmt->close();
$conn->close();


} else{
    echo "All fields are required";
    die();
}
?>

Please can anyone let me know if my code is wrong or if there is something I’m missing out on here.