Stripe Checkout but for file uploads?

Not sure where to ask this, so will try here.

I'm looking for something like Stripe Checkout but for file uploads. Is there anything like this? The closest I found was Filestack, yet it seems it can't do what I'd need, which is a workflow like:

1. Open website and call the File API
2. Get a link the user can go to and upload files from
3. The user can switch from e.g. Desktop to Mobile easily with a QR code
4. The files are uploaded and can be automatically transformed (e.g. images to PDF)
5. My app receives a webhook event with some metadata

I'd appreciate any recommendations!