MailChimp for WunderAutomation provides a trigger that can handle incoming webhooks from the MailChimp service. MailChimp describes how to set up a new webhook here.
This trigger has only one field
|A unique string that identifies this webhook. When first selecting this action, a random code is generated.
You can edit the identifier if you prefer a different UR, but note that you can only use lower case characters a-z, 0-9, – (dash) and _ (underscore).