Vouchers are an optional concept in Next only used as an image container, it is not an accounting document header. A voucher row contains all the required information about costs and revenue independently, without referencing a header/voucher. If you don't have an image, you can go ahead and create the rows direcly using the POST
/voucher/row/ endpoint without first creating a voucher.

Group voucher rows together

If you want to have a common reference for a set of voucher rows, for example to know which voucher rows belong to a common header in the accounting system, you should use the vouchernumberfield in the POST /voucher/row/ endpoint for this purpose.

Using optional vouchers

It is possible to attach PDF:s or URL:s to voucher rows in Next. This is highly appreciated by the user since it will make it possible to preview supplier invoices directly from Next. PDF:s can then be attached to a customer invoice or a report, but the URL will only be a fast-track to the PDF in an external system.
To be able to connect a PDF file to a voucher row, a voucher object needs to be created. This can be done according to below:

Create a voucher using the POST/voucher/ endpoint and add the PDF/picture to the voucher
In the response there will be a field voucherid
Create voucher rows using the POST/voucher/row endpoint and associate them to the voucher using the voucherid.
The PDF/picture will now be available for all rows associated with the voucher in Next under the tab Booked cost/revenue.