Undefined array key when post data in PHP

I have a Database with 3 tables, in this error I’m only using table Customers.

Table Customers has 4 rows: id_customer, fn_customer, ln_customer and email_customer.

I’m making a form in file InsertCustomers.php so I can insert data in this table. The problem is when I click to submit data this error appears: Undefined array key.

This errors appears in this 3 lines:

$input_fn = trim($_POST["fn_customer"]);
$input_ln = trim($_POST["ln_customer"]);
$input_email = trim($_POST["email_customer"]);

This is the a portion of the code:

// Include config file
require_once "../connectDB.php";
 
// Define variables and initialize with empty values
$fn_customer = $ln_customer = $email_customer = "";
$fn_customer_err = $ln_customer_err = $email_customer_err = "";

// Processing form data when form is submitted
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    // Validate name
    $input_fn = trim($_POST["fn_customer"]);
    if (empty($input_fn)) {
        $fn_err = "Please enter a name.";
    } elseif (!filter_var($input_fn, FILTER_VALIDATE_REGEXP, array("options" => array("regexp" => "/^[a-zA-Z\s]+$/")))) {
        $fn_err = "Please enter a valid name.";
    } else {
        $fn_customer = $input_fn;
    }

    if ($_SERVER["REQUEST_METHOD"] == "POST") {
        // Validate name
        $input_ln = trim($_POST["ln_customer"]);
        if (empty($input_ln)) {
            $ln_err = "Please enter a name.";
        } elseif (!filter_var($input_ln, FILTER_VALIDATE_REGEXP, array("options" => array("regexp" => "/^[a-zA-Z\s]+$/")))) {
            $ln_err = "Please enter a valid name.";
        } else {
            $ln_customer = $input_ln;
        }
    }

    if ($_SERVER["REQUEST_METHOD"] == "POST") {
        // Validate name
        $input_email = trim($_POST["email_customer"]);
        if (empty($input_email)) {
            $email_err = "Please enter a email.";
        } else {
            $email_customer = $input_ln;
        }
    }
...

I tried var_dumping and trying to isset get this data, but it didn’t work.

>Solution :

Probably fn_customer, in_customer and email_customer index do not exist on $_POST var.

You can validate then using isset, for example:

if(isset($_POST['desired_index')) {
   // Your code
} else {
  // An error
}

This solve the form validation.

I just saw your code in source. The problem is in the name of the inputs. Just rename then like this:
fn_customer -> fn, ln_customer -> ln, email_customer -> email