Need help in connecting drop box API

The Dropbox API does not offer a way to get an access token just by exchanging the app key and secret. The app key and secret only identify your app itself. In order to access a Dropbox account, the app needs authorization from the account owner. 

Typically, to get authorization from the user and receive an access token for the end-user, the app should implement and use the OAuth app authorization flow. You can find information on how this works in the OAuth Guide.

Note that if you only need to access your own account though, you can just manually get an access token for your own account once and then store and re-use that for API calls to your account without further manual intervention. Make sure you don't expose your access token to other users though.