I recommend trying this in the UI first, if you haven't already. Once it works in the UI, please write the workflow using the Screen IDs. This will make it easier for me to assist you with how to do this using the API. The information below comes from the UI documentation on adding a purchase order to supplier invoice, and on how to use Link Line. My first thought is that the “require receipts” could be the cause for this “cannot be found in the look-up table”- error.   ... View more