How can I use GPTs file feature to upload directly to my own API?

Does anyone know how to send directly to our API via GPTs upload file function? How to use the URL after uploading a file?

Our team is currently building a GPTs that requires users to upload a file, send the URL to our API, and then return relevant new content. However, sending GPTs currently does not work directly with the URL of the uploaded file.

There is no published available URL for files uploaded, that would be a giant security risk.