No webhook notification received on dropbox content change

Webhook notifications only fire for changes in accounts linked to your app (that is, accounts that users have authorized the app to access). Are you making changes in an account linked to your app?

I have created a dropbox account and an app. As I did not find anything about linking in the tutorial, I supposed that they were linked. Could you let me know how to link the app to my dropbox? Thanks.

Exactly how you link your app to an account depends on the specifics of your setup. E.g., what SDK or library are you using, if any? In general though, you should work through the tutorial for whatever SDK or library, as that should show you how to get started.

Also, the OAuth guide may be helpful:

https://www.dropbox.com/developers/reference/oauthguide

I am only trying to use webhooks, so should I take a look in one of the SDK tutorials?

Can you elaborate on what you mean when you say you're only trying to use webhooks? What are you trying to build?

In the meantime I clicked on OAuth2/Generate token, and everything started to work. Can it be?
First I am trying to get to know any changes in a dropbox folder, then I will also need to get/send files as reaction to the changes.

If you only need to know about changes in your own account, that's fine. Generating an access token on your app's page links the app to your own account. (To link the app to any other accounts though, you'd have to implement the OAuth app authorization flow as shown in the OAuth guide.)