Heroku error while attempting to deploy the application from the drop box


I am trying to deploy a node app on heroku via the web GUI for dropbox, and I get the error:

Item could not be modified:

    "Content-Type" request header must be set to "application/json".

Any clues as to what that might mean?

Disclaimer: I was not the one who wrote the app, just made two mods for heroku.

In case you haven't found an answer... I have the same problem. You probably need to update your runtime stack.

Here's Heroku's message on their website: "The legacy Cedar-10 stack has been deprecated and reached its end-of-life on November 4, 2015. Applications may continue running, however you will not be able to push to your application without upgrading to Cedar-14 first."

How to update informations are available here: https://devcenter.heroku.com/articles/cedar-14-migration#upgrading-the-production-app-to-cedar-14