Validate and deduplicate webhook leads into a Google Sheets review queue

Description

Quick overview
This workflow receives lead data via a webhook, normalizes and validates required fields, and then writes valid, de-duplicated leads to Google Sheets while routing invalid payloads to a separate Review Queue tab.

How it works
Receives a POST request on a webhook endpoint with lead data in the JSON body.
Normalizes key fields (for example, trims and lowercases the email) and adds a received timestamp.
Validates the payload by checking for a correctly formatted email address and a non-empty source ID.
Appends invalid submissions to a Google Sheets “Review Queue” sheet with the failure reason and original values.
Looks up the source ID in a Google Sheets “Records” sheet to determine whether the lead already exists.
Appends a new row to the “Records” sheet only when no existing row with the same source ID is found, otherwise it skips creation.

Setup
Create a Google Sheets OAuth credential in n8n.
Create a spreadsheet with two tabs named “Records” and “Review Queue”, and ensure the “Records” tab includes a “source_id” column for lookups.
Replace REPLACE_WITH_YOUR_SPREADSHEET_ID in the Settings step with your Google Sheets spreadsheet ID.
Copy the production webhook URL for the “intake” endpoint and configure your form/app to POST JSON containing at least id (source ID) and email (optionally name).

Requirements
A Google Sheets OAuth2 credential, and any source that can POST JSON to a webhook, such as a web form, CRM or app.

Customization
Swap Google Sheets for your own CRM or database. The routing logic is what matters, not the storage.