The problem has been described here already:
Tl;Dr: The slack trigger gets triggered by bot messages even if the filter “trigger for bot messages” is set to False.
It’s CRAZY that this is a 2 years old bug and you haven’t fixed it! This could financially ruin people if they use paid APIs in the zap.
FIX IT ASAP.
Hi 
Yikes! I looked into it and you’re totally right, the bug report for that issue is still open. I can’t share any ETA on when it will be fixed but I’ve added you to the list of affected users so that we can notify you by email the minute it gets resolved.
There is a workaround mentioned on that existing topic to use a Filter by Zapier action to only allow the Zap to continue to run subsequent actions if the value in the is_bot field is (Boolean) Is false. Which should help to prevent the Zap from using up tasks unnecessarily. One thing to bear in mind with this is that adding a filter to the Zap would make it a Multi-Step Zap. So if you’re not on a paid plan that wouldn’t be a viable workaround.
That said, I did see a couple of reports from folks writing into Support where setting the “Trigger for Bot Messages?” was to “Yes” and it actually had the opposite affect and prevented the Zap from triggering on bot messages. It’s not clear if something got mixed up on the settings or whether that was just a temporary glitch that produced that behaviour. Not sure if that is still the case but may be worth trying it out on your Zap to see if setting it to Yes instead of No would get it to ignore bot messages while the bug is still unresolved.
If you do give that a try and it works please let us know!
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