Show the payemnt page URL in the admin page of the order.

functions.php

/**
 * Show the payemnt page URL in the admin page of the order.
 *
 * @param object $order
 * @return void
 */
function wc_admin_show_payment_url( $order ) {
    if ( $order->get_status() != 'pending' ) {
        return;
    }

    ?>
    <p class="form-field form-field-wide">
        <label for="order_pay_url"><?php _e( 'Payment URL:', 'woocommerce' ) ?></label>
        <p id="order_pay_url"><?php echo make_clickable( esc_url( $order->get_checkout_payment_url() ) ) ?></p>
    </p>
    <?php
}
add_action( 'woocommerce_admin_order_data_after_order_details', 'wc_admin_show_payment_url' );