I can't do the Casey's pizza party quest

[Crevetted'eaudouce]

To summarize i got the quest and i went to him with the path under the bridge and from what i know the figth starts by going to him trougth the sewers and now that i take this path the fight does not start but maybe i'm wrong and that's not how the quest starts.
so if you know how to starts the quest tell me or if it's a bug.

[Bercerveza]

its a bug, i had the same problem and i replay it