Code snippet to allow customers to pay for an order without logging in.

no_login_order_payment.php

<?php


/**
 * Allow orders created by an admin to be paid without the user logging in.
 *
 * @param array $allcaps All capabilities of the user.
 * @param array $caps    Capabilities requested.
 * @param array $args    Extra Arguments.
 *
 * @return array The filtered capabilities of the user.
 */
function jp_custom_order_caps( $allcaps, $caps, $args ) {
	if ( ! isset( $caps[0], $args[2] ) ) {
		return $allcaps;
	}

	switch ( $caps[0] ) {
		case 'pay_for_order':
			$order = wc_get_order( $args[2] );
			if ( 'admin' === $order->get_created_via() ) {
				$allcaps['pay_for_order'] = true;
			}
			break;
	}

	return $allcaps;
}
add_filter( 'user_has_cap', 'jp_custom_order_caps', 10, 3 );