Problem with PayPal Sandbox test (UK) - BAD_INPUT_ERROR

[INVALID_BUSINES]

I'm new to PayPal and am trying to integrate a very simple checkout into my website. Sadly, the Sandbox keeps throwing up error after error. The following is the code I'm sending but it's based on a 2020 guide. Any idea what I'm doing wrong?

<?php

// For testing purposes set this to true, if set to true it will use paypal sandbox

$testmode = true;

$paypalurl = $testmode ? 'https://www.sandbox.paypal.com/cgi-bin/webscr' : 'https://www.paypal.com/cgi-bin/webscr';

// If the user clicks the PayPal checkout button...

if (isset($_POST['paypal'])) {

    // Variables we need to pass to paypal

    // Make sure you have a business account and set the "business" variable to your paypal business account email

    $data = array(

        'cmd' => '_cart',

        'upload'        => '1',

        'lc' => 'EN',

'business' => 'xxxxxxxxxxxxxxxxxxxxxxx',

        'cancel_return' => 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.php?mode=cancelled',

        'notify_url' => 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.php?page=cart&ipn_listener=paypal',

        'currency_code' => 'GBP',

        'return'        => 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.php?mode=confirmed',

'item_number_1' => '$id',

'item_name_1' => '$name',

        'quantity_1' => '1',

'amount_1' => '$price'

    );

    // Send the user to the paypal checkout screen

    header('location:' . $paypalurl . '?' . http_build_query($data));

    // End the script don't need to execute anything else

    exit;

?>

Thank you so, so much in advance.