Show the order payment URL on the admin order page

functions.php

add_action( 'woocommerce_admin_order_data_after_order_details', 'woo_show_order_payment_url' );
function woo_show_order_payment_url( $order ) {
	echo '<a href="' . $order->get_checkout_payment_url() . '" title="' . __( 'Get order payment URL', 'your-domain' ) . '" target="_blank">' . __( 'Get order payment URL', 'your-domain' ) . '</a>';
}