In order to vouchers between WooCommerce and Epos Now, we recommend using a service that is built to integrate with both platforms. Our customers currently use
VoucherCart to integrate their vouchers and keep them in sync.
Orders can then be paid for on the website with the voucher, and Slynk picks up the order once it is in WooCommerce (it does not affect us how the order was paid for as long as we can see the order in WooCommerce) and sync it to EposNow.