Can I save a JSON stream object to Dropbox file with Dropbox Post Rest API ?

Just set the Authorization header to Bearer <token>. The documentation doesn't mention this, because it's just how OAuth 2 works.

BTW, I redacted the access token in your post, but just in case someone else saw it, you should make sure to disable it. Unlinking your app from the account security tab and then relinking (getting a new token) should do the trick.