Based on the instructions you linked to, you should click the "Authenticate" button in the Qlik product to begin the Dropbox authorization flow. Have you tried this, and if so, what happened?
If something doesn't appear to be working correctly on dropbox.com itself, please let us know the details.
Otherwise, if you need help configuring Qlik, please reach out to Qlik for help. We can't offer help with Qik itself as it's made by a third party.