Give_Payment::get_meta PHP Method

    public function get_meta($meta_key = '_give_payment_meta', $single = true)
    {
        $meta = get_post_meta($this->ID, $meta_key, $single);
        if ($meta_key === '_give_payment_meta') {
            if (empty($meta['key'])) {
                $meta['key'] = $this->setup_payment_key();
            }
            if (empty($meta['form_title'])) {
                $meta['form_title'] = $this->setup_form_title();
            }
            if (empty($meta['email'])) {
                $meta['email'] = $this->setup_email();
            }
            if (empty($meta['date'])) {
                $meta['date'] = get_post_field('post_date', $this->ID);
            }
        }
        $meta = apply_filters('give_get_payment_meta_' . $meta_key, $meta, $this->ID);
        return apply_filters('give_get_payment_meta', $meta, $this->ID, $meta_key);
    }

/**
 * Update Old Payments Totals
 *
 * Updates all old payments, prior to 1.2, with new meta for the total purchase amount.
 *
 * It's done to query payments by their totals.
 *
 * @since  1.0
 *
 * @param  array $data Arguments passed.
 *
 * @return void
 */
function give_update_old_payments_with_totals($data)
{
    if (!wp_verify_nonce($data['_wpnonce'], 'give_upgrade_payments_nonce')) {
        return;
    }
    if (get_option('give_payment_totals_upgraded')) {
        return;
    }
    $payments = give_get_payments(array('offset' => 0, 'number' => -1, 'mode' => 'all'));
    if ($payments) {
        foreach ($payments as $payment) {
            $payment = new Give_Payment($payment->ID);
            $meta = $payment->get_meta();
            $payment->total = $meta['amount'];
            $payment->save();
        }
    }
    add_option('give_payment_totals_upgraded', 1);
}