Pagination to a streamsets pipeline throws null pointer exception

Trying to add pagination to a streamsets pipeline that requests data from Tableau. Currently, the API is of the format: ttps://us-west-2b.online.tableau.com/api/3.3/sites/${record:value('/credentials/site/id')}/workbooks?pageNumber=${startAt} , where startAt starts at 1 and should go to 4. I selected the "By Page Number" pagination mode option with an offset of 1. However, I am getting a null pointer exception on making the request.