Being able to have a merge field to add direct links in messages that take the recipient to the invoice where payment information exists. For QBO's API, two interesting returns exist that are worth looking into: Get an invoice as PDF: This resource returns the specified object in the response body as an Adobe Portable Document Format (PDF) file. The resulting PDF file is formatted according to custom form styles in the company settings. and Read an invoice: Retrieves the details of an invoice that has been previously created.