Yes, so in this case, uploading files will need to be done locally (meaning you need to first download the file to your local machine, and then include the path in your machine in your request).
Based on the flow you’ve included, it seems like this is the route you’re going down. I think the best way to troubleshoot this would probably be to go step by step.
I would make sure that the file is indeed a local file, and then having done that I would attempt to utilize a different platform (maybe something like Postman which is my go-to) to see if I can upload this local file myself.
As a reference, I would definitely check out my colleague Alex’s example here.
Good luck and let me know if this helps you isolate the issue a bit more!