What is the initial incident in "The Cask of Amontillado"?

In my opinion, the initial incident in this story is not really even seen in the story.  To me, the initial incident is whatever Fortunato did in the past to Montresor.

The initial incident is the thing that leads to the rising action in the story.  To me, the rising action in this story is the interaction between Montresor and Fortunato as Montresor maneuvers Fortunato into going down into Montresor's wine cellars.

So the initial incident has to be whatever caused this to happen.  In my opinion, that is the conflict between them that is only referred to in this story.