Attach a PDF when sending email via Outlook - SOLVED

I’ve built an integration to generate a pdf file from a Jotform form submission using PDFMonkey. Everything works except the final step where I need to attach the PDF file using the supplied download URL. I can embed the URL directly in the body of the email and if the recipient clicks on the URL they can download the document but I’d like to have the PDF be an attachment. The URL expires after an hour so it’s not a good solution.

When I attempt to get this to work (see screenshot) I get the error shown.

Can anyone help me debug this please?