How to correctly setup Events and happenings inside Journeys?

Summary:

Hi,

We would like to understand better events and happenings, but we do not find any more info on the documentation than this:

Would it be possible to explain which URL needs to be added? We have tried external URLs and it does not work:

Thanks.

Kind regards,

Pilar

Version (include the version you are using, if applicable):

25 B