Excel: Insert data table into Excel template - does template need to be a pushbot level field?

I am building a workflow in which an Excel file is downloaded from Sharepoint, then data is added to this Excel file, and lastly it is re-uploaded to Sharepoint. Since I did not have Sharepoint integration experience, I first was working on the many steps for "adding data" to the Excel, and just started with the Excel file as a "pushbot level field" (i.e. to get around not knowing the Sharepoint actions, the workflow at first did not download anything from Sharepoint, the Excel file was already in the workflow as a default value in a pushbot level field). So I got the "adding data" steps to work smoothly, and then I separately worked on and successfully built the Sharepoint download and upload steps. Now when I add the Sharepoint download step at the front end and have the workflow use the downloaded Excel file instead of the default file from the pushbot level field, the Action: Excel: Insert a data table into an Excel template (which I use as part of the "adding data" steps) throws the following error: "The action was unable to process this spreadsheet. Please contact Catalytic at help@catalytic.com."

Question: Does this Action only work with Excel files that are in a pushbot level field? I kind of think so because of the word "template" in the Action name. I am not really using a template, it is a file that is downloaded within the workflow in a previous step.
Thank you!