Scrivener won't open file from Dropbox

I am new to Scrivener so I’m not sure if this is a user error. I created a project in scrivener, imported the files I wanted to work on from Dropbox, edited them, and then synced the project as .txt files in the Dropbox folder. I then worked on them in iawriter on the iPad. Now Scrivener won’t let me open the project file. The “Open” button is grayed out.
I tried to rename the folder with a .txt.scriv extension thinking that might be the problem but it just gave me an error message.

Once you turn them into .txt files, what you have is no longer a Scrivener project. It’s a collection of .txt files. To work with these files in Scrivener, you would need to use the File -> Import -> Files command.

The solution is to use Scrivener’s “Synchronize with External Folder” feature, discussed in Chapter 13 of the Scrivener manual. As the name suggests, that feature is designed to allow you to work on Scrivener projects using other programs, then automatically import the results back into Scrivener.