I have a Nintex Workflow that takes the attachments from the Nintex Form and uploads them into a document library using the Office 365 upload. I originally was doing this through Java, but I wanted to get rid of the java and do it through a workflow now. However I want to update the lookup field in the document library list with the associated title and data from the SharePoint list I am uploading the documents from. However I get the following error when I try to set the lookup field in the document library with the linked item in the list.

I am doing it this way because I already have the lookup field in the document library and I want to keep using it.