So, I misread the computer requirements for Scrivener 3, and I am so glad I did! If you have Mac El Capitan (10.11.something) , and can only download Scrivener 2, it IS still possible to sync with the mobile app! Here is what I did:

1. Purchase Scrivener 3 (The key still works on Scrivener 2, and if you upgrade you can use the same key for Scrivener 3)

2. Purchase the Mobile app and connect it with Dropbox (make a mental note of which folder Scrivener creates for its files)

3. Download Dropbox on your Mac

4. If you drag a Scrivener 2 file from your Mac into the SAME dropbox folder Scrivener for mobile uses, it will appear on the iPad when you sync. (Make sure the file ending is still .scriv - for some reason when I uploaded it to dropbox in my browser it became a zip file instead. It worked when I put it in the matching file on my computer.)

5. If you open a file you created on the iPad from the dropbox folder on your computer, Scrivener 2 can open it.

I have not come across any incompatibilities in the file formats yet, but I just got it set up. It appears that the only difference is that I have to manually save my Scrivener 2 files in the Dropbox folder on my computer (which then automatically syncs with Dropbox online) Let me know if you have any questions, or if you find certain features that don't work between Scrivener 2 and the mobile app.

As someone who is resisting the change to computer programs by subscription, (and either the headache of bouncing between two computers, or the expense of upgrading) I was very glad to find this workaround so I could keep all the programs I have for El Capitan! I believe this is the last Mac operating system to have Adobe without a subscription cost.