Get amount from url (anchor link fix)

get_amount_from_url.php

<?php 
add_action('givewp_donation_form_schema', function($form) {

    /** @var \Give\Framework\FieldsAPI\Amount $field */
    $field = $form->getNodeByName('amount');

    if (!$field) {
        return;
    }

    $defaultAmount = $field->getDefaultValue();

    // Direct query string
    if (isset($_GET['amount'])) {
        $defaultAmount = (float) give_clean($_GET['amount']);

    // Referrer fallback
    } elseif (!empty($_SERVER['HTTP_REFERER'])) {

        $urlParts = parse_url($_SERVER['HTTP_REFERER']);

        if (!empty($urlParts['query'])) {
            parse_str($urlParts['query'], $query);

            if (!empty($query['amount'])) {
                $defaultAmount = (float) give_clean($query['amount']);
            }
        }
    }

    if ($defaultAmount === $field->getDefaultValue()) {
        return;
    }

    $field->defaultValue($defaultAmount);

    if (!empty($field->getFixedAmountValue())) {
        $field->fixedAmountValue($defaultAmount);
    }
});