I really think for the price we pay for service this should really be an option.
Welcome to the Community, @MCCo -
At the moment, this would be a Feature Request for our Product Team. Being able to have the customer upload a file on there end isn't possible, even with a subscription.
I would recommend adding this Feature Request to our Ideate Board. Once more information becomes available, a Community Moderator will go to your post & update the status to keep you in the loop.
Thank you for bringing this to us!
Square Community