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.
*Later, trying again from the computer*
Google what the fuck does "Processing" mean. What does it mean to process a book. I just want you to sync it to my phone and open it. I mean it's already on my phone but you won't open it on my phone unless you first sync it from my phone to your server back to my phone so I'm trying to be accommodating.
If I click on the book all it does is open a new tab containing this help page https://support.google.com/googleplay/answer/185545?visit_id=638955591931852971-3016000300&rd=2
Has anyone ever seen Google Play Books do this, and if it does, is there a way to get an error message? I am in contact with¹ the publisher but there is not enough information to tell the publisher what is wrong.
¹ Married to
Alternately I am now looking for recommendations for a good basic epub reader for Android. All I want is for it to have text search, have a good upper range of font sizes, and not display "noise" such as page numbers or the current time while I am reading. I have never needed anything besides Google Play Books before this.
@glyph What does it mean that google play says this "contains ads"
@mcc Oh. It's "remove ads" software. Open source though so if you don't want to pay for it, you can build your own copy:
https://github.com/foobnix/LibreraReader 
GitHub - foobnix/LibreraReader: Book Reader for Android
Book Reader for Android. Contribute to foobnix/LibreraReader development by creating an account on GitHub.
GitHub@glyph I think the intersection of "running an ad engine, which does goodness knows what" and "requires full access to all files to run" might be over my risk budget… maybe I'll look at self compiling later :/
@mcc I was just looking for open source ones with reasonable presentation. I would not heavily endorse it particularly if you have lots of other options. Sadly the one I actually used to use has been dead for many years now. (I still fondly remember it using the volume buttons for pagination and I am *still* kind of mad that no iOS e-reader does this yet.)