Hello Mrs t. Sorry to hear you are having issues with your Vox.
I think it's best to start at the least drastic solutions first. You've already done the first step--turning the Vox off and on. (It's surprising how many electronics problems that step solves!
) If you were able to sign out of your Kobo account on the Vox itself and then sign back in, I would try that next, but if the app is giving you an android error, it sounds like you might not be able to do that. My Vox has been shut down and set to factory state, so I don't have access to it to be able to tell you if there is a way to sign in and out of Kobo without using the Kobo app. And this sounds like an issue with the Kobo app rather than it being a case of it not being able to connect to your Kobo account.
You could try the reset button. If you carefully peel the back off the Vox, you will see a little black button just above the upper right corner of the battery. Push that button. This won't do any harm and you won't lose any data from the device. It's like doing a computer reboot.
If that doesn't work, I would suggest you contact Kobo help using their online chat service. This will get you the quickest results, and they'll e-mail you a transcript of the chat session afterwards as well:
http://kobo.frontlinesvc.com/app/ask
They'll be able to walk you through more things you can try.