Here’s a list of all Triggers available with the Slack integration:
You can access data from any of these Triggers by reading event.payload after the Trigger fires.

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Reaction Added

This Trigger executes whenever a reaction is added to a message in a channel that your bot is a member of. It receives the slack:reactionAdded event and returns the following payload:
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payload
object

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Reaction Removed

This Trigger executes whenever a reaction is removed from a message in a channel that your bot is a member of. It receives the slack:reactionRemoved event and returns the following payload:
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payload
object

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Member Joined Channel

This Trigger executes whenever a new member joins a channel that your bot is a member of. It receives the slack:memberJoinedChannel event and returns the following payload:
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payload
object

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Member Left Channel

This Trigger executes whenever a new member leaves a channel that your bot is a member of. It receives the slack:memberLeftChannel event and returns the following payload:
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payload
object

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Member Joined Workspace

This Trigger executes whenever a new member joins the Slack workspace that your bot is installed to. It receives the slack:memberJoinedWorkspace event and returns the following payload:
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payload
object