Here is how I see the Zap for the workflow that you have in mind:
Trigger: Gmail (New Email Matching Search)
Filter by Zapier *to ensure that the email contains a CSV attachment
Action: Webhooks by Zapier (Custom Request)
I want to be upfront with you that Webhooks by Zapier is considered an advanced feature, so our support for it may be more limited. This is because APIs can be so different, and each request can be so unique, making it challenging for us to determine why a request may not work as expected. However, if you need help setting up the Webhooks by Zapier step, you can reach out to one of our certified Zapier Experts here: https://zapier.com/experts.