It is possible for you to retrieve all previous invoices either through the API or through the dashboard. A link to the invoice is stored in the transaction data as a URL in the transaction.invoice_image_url field.
The invoice_image_url is a link to an HTML file, but if you have enabled PDF invoice generation you can also replace ".html" with ".pdf" in the url to access the PDF version of the document.
Invoice documents can be either be saved locally as a PDF or HTML file in your own system, or you can provide the URL directly to your customers.
Updated 7 months ago