Dropbox is in the process of switching to only issuing short-lived access tokens (and optional refresh tokens) instead of long-lived access tokens. You can find more information on this migration here.
Apps can still get long-term access by requesting "offline" access though, in which case the app receives a "refresh token" that can be used to retrieve new short-lived access tokens as needed, without further manual user intervention. You can find more information in the OAuth Guide and authorization documentation.
For reference, 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, if you have any. Also, note though that after the change you won't be able to create new long-lived access tokens.
Either way though, whether using a legacy long-lived access token or short-lived access tokens with a refresh token, this isn't something you would plug in to Dropbox itself. The use of access tokens/refresh tokens occurs in the third party code. That is, the third party app itself would be the one to have and store the access token/refresh token, which it then uses to perform the API calls. So, you would need to update the configuration in the third party app.
Note that this is something that would need to be implemented by the programmer of the app though, so if you are not the
programmer responsible for this integration, you may need to get an update from them to support this.
