Access Token is invalid in android

The authenticationSuccessful is only meant for use during the actual app authorization flow, when the user chooses whether or not to authorize the app. That being the case, it will only return true during that first session.

If you just want to know if you have an access token, you should use isLinked.

By the way, I redacted it, but you publicly posted a valid access token, so for the sake of security, you should disable it. You can do so by revoking access to the app entirely, if the access token is for your account, on your account security page.

Or, you can disable just this access token using the API:

v1: https://www.dropbox.com/developers/core/docs#disable-token
v2: https://www.dropbox.com/developers/documentation/http/documentation#auth-token-revoke

Finally, I should note that the Android Core SDK you're using uses API v1, which is deprecated. You should migrate to API v2. You can use the API v2 Java SDK for that.