zapier is unable to send challenge value to enable slack event api

I'm using zapier with slack and want to catch an event when message_replied event was created as referred here.

To use event API, it needs URL verification, which is unable on zapier webhook catching. The following error occurs repeatedly; Request URL Your URL didn't respond with the value of the challenge parameter.

Are there any workarounds? I'd really appreciate any help you can provide.

some related informations:

app used in zapier : Webhooks by Zapier
Event in zapier : Catch Hook
feature used in slack bot : Event Subscriptions

Solution

This is not currently possible. "Webhooks by Zapier" will only respond with the default "success" response because it's intended to be used with any incoming webhook. For that product, there's not special cases for any particular service.

If you're trying to integration with the Slack Events API (something I implemented at Zapier), then I recommend writing your own web service to catch Slack hooks, do business logic, and then send relevant webhooks onto Zapier as needed. This will afford you much more control over the process.