Getting GPT Assistant to upload files via API

I have a use case where I want to the GPT to ask me to upload a file and then use that file to upload to another API for processing.

I’ve managed to get the GPT to ask me for the file which I upload but trying to find a method to upload that file into a API which seems very hard to do.

Using Zapier API but it does nothing but upload the file name into a blank file.

Has anyone managed to get a API working which accepts file uploads from GPTs or any workarounds?