Hi we have an old dropbox OAuth app with auth token expiration key : no expiration. As now you want us to moved to short-lived tokens , if we update the old oAuth app's expiration to short live will it affect existing long lived tokens ?
No, it will NOT affect the existing long lived tokens, if any. Take in mind that if existing long lived token gets revoked (when application is gonna reinstall, for example; not just update with reusing of existing configuration) then only short lived token (together with refresh token) could be used from that moment on.
Здравко is correct, while the creation of new long-lived access tokens is now deprecated, we don't currently have a plan to disable existing long-lived access tokens. (If that changes, we will of course announce that ahead of time.) That being the case, you can continue using existing long-lived access token(s) without interruption. Just note that you won't be able to create new long-lived access tokens.