Use Invoice with Modal Box
To connect the created Invoice with the payment (Transaction), you must use the
linkprovided in the response from POST as
hrefof your modal box markup or build it yourself from the also provided
referenceIdfor that purpose will not work as expected, even when the demo results suggest that in some vague way.
Connecting your application with our Shop & Pay payment
If you have set up a webshop and would like to integrate Shop & Pay as your payment solution then it is necessary for you to create an invoice in the Shop & Pay system which you can then display as a payment form to the customer.
The response generates an Invoice ID which you can use to identify the successful payment. (see the chapter "Webhooks" for more information)