I'm at the laundromat. I have a 20mb epub in my Dropbox. I try to open it in the Dropbox app. It goes, I can't open this, but here's a button to upload it to Google Play Books. That's convenient, I think; I tap it. It spends something like twenty minutes downloading the epub to the phone over a cell connection, then another twenty minutes uploading it to Google Play Books. Eventually it finishes. I open Google Play Books. The book is not there. Nor is it in Files. There is no error message.