Something very strange is happening to me. I generate a new token, but after a few hours only this token is disabled. In addition, I try to pass the app to production and it does not let me exit the Development mode.
What do I do more? How can i fix this? Thanks
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.
While the change began on September 30th 2021, we're releasing it gradually, so you may not have seen your app(s) affected until now. Once it applies to your app, it would apply regardless of the "Access token expiration" setting for your app, and that setting may no longer be available for your app.
Also, it looks like you've used the "Generate" button to create a short-lived access token for your app. In order to apply for "production", you should implement and test the OAuth app authorization flow first. You can find more information on applying for production here.