I wrote about it in another thread… Compatibility with SONOFF 433 RF BRIDGE MHZ and SCENE/WebHook - #4 by morgan
The application and account in the free version do not have webhooks, this is a feature only for the paid plan and is only available via WEB. Even if we have an account with a paid plan, we will not see this function in the app. I speculate that this is a functionality assigned to the WEB structure and not per account, and access to the WEB is per account.
In short, someone in the company decided that it was supposed to be like that, or didn’t think through the function pattern. 