Hey @thiagonascimentodf!
I was trying to achieve something similar to this with Twitch and below is the workflow I used to verify the challenge.
Once the challenge is verified you can remove the Set node, and replace it with the Send Email node.
To help you better understand, these services require us to send back the challenge as a string. The Set node gets that challenge from the Webhook node. The ‘Last Node’ Response Mode, uses this value from the Set node to send back this challenge and verify the URL. You can read more on how to send a string response type for webhook here.