Sorry, I had skipped adding of access and secret key. Now it generates no error. But the Dropbox pop up window reads the following error.
Error (400)
It seems the app you were using submitted a bad request. If you would like to report this error to the app’s developer, include the information below.
More details for developers
Invalid redirect_uri: “https://erp.kordindia.com/api/method/frappe.integrations.doctype.dropbox_settings.dropbox_settings.dropbox_auth_finish”: It must exactly match one of the redirect URIs you’ve pre-configured for your app (including the path).