Copilot Agent - Pass uploaded attachments to Power Automate

I have an agent with a topic which asks the user to upload photos. I stored these photos in a file variable. My idea is to trigger an HTTP Request which triggers a Power Automate flow and manipulates the files as needed. 
Has anyone successfully achieved triggering a flow and passing any information? Not seeing information or guides on this issue specifically.

I currently receive a 403 Forbidden error on my attempts at a POST HTTP Request.