GMBFlow: automate Google review requests with n8n, Gmail, and a Next.js dashboard

Asking for Google reviews is easy to postpone and painful to do well. Blast everyone the same link and you train customers to ignore you; let unhappy buyers hit your public listing and one bad afternoon becomes a permanent scar. The naive fix, a shared Google review URL in a footer, skips the rating filter entirely and gives you no queue, no duplicate guard, and no record of who already responded.

This guide builds GMBFlow, a Next.js dashboard backed by three n8n workflows. You onboard businesses, tag leads by service, queue branded review emails, and collect ratings on a dedicated review page. Four and five stars redirect to Google Business; one to three stars stay internal. Already-reviewed leads cannot be re-queued or re-submitted. The important design decision is the rating split on the review page itself, before anything public happens.

Available resources#

This build uses four assets you will set up below:

1. n8n workflow "GMB 00: Bootstrap Data Tables" (creates five data tables idempotently).
2. n8n workflow "GMB 02: Send Review Email" (Gmail sub-workflow called when a lead is queued).
3. n8n workflow "GMB 01: API Gateway" (all app CRUD, review submission, and email job dispatch).
4. GMBFlow app (Next.js dashboard at /b/{slug} plus branded /review/{token} pages).

What you'll need#

Before you begin, make sure you have:

1. An n8n instance (cloud or self-hosted) with Data Tables enabled and a public HTTPS webhook URL.
2. A Gmail account with a Google Cloud OAuth app authorized for gmail.send.
3. An n8n API key so the API Gateway Code node can read and write Data Tables via the REST API.
4. A shared GMB API key (sent as X-API-Key) that both the Next.js app and n8n workflows agree on.
5. The GMBFlow Next.js app cloned locally (bun install, then bun dev on port 3000).
6. A Google Business Profile place ID for each business you onboard (used to build the public review redirect URL).

Overview of the automation#

The automation runs in three phases. The Next.js dashboard is the UI; n8n is the backend.

1. Bootstrap storage. A one-time workflow creates five n8n Data Tables that hold businesses, services, leads, reviews, and activity logs.
2. Queue and send. The dashboard queues leads via the API Gateway. The gateway marks them queued, then calls the email sub-workflow, which sends a Gmail message with a branded /review/{token} link.
3. Collect and filter. The customer submits a 1 to 5 star rating on the review page. Four and five stars unlock a redirect to Google Business; one to three stars are saved internally only.

Splitting the API Gateway from the email sub-workflow keeps the webhook response fast. The gateway acknowledges the queue request immediately, then fires Gmail sends asynchronously with a five-second stagger between batch items so you do not trip rate limits.

Step-by-step setup#

1. Set up the Data Tables#

GMBFlow stores everything in five n8n Data Tables. Column definitions live in the GMBFlow repo at n8n/tables-schema.json.

Bootstrap via webhook (recommended). Import gmbflow-00-bootstrap-tables.json, activate it, then trigger:

curl -X POST https://your-n8n.example.com/webhook/gmb-bootstrap-tables

The workflow is idempotent: existing tables are left untouched. After bootstrap, copy each table ID from n8n into n8n/gmb-config.json in the GMBFlow repo (start from gmb-config.example.json).

2. Connect credentials in n8n#

Add these before importing the remaining workflows:

1. Gmail OAuth2 in Google Cloud Console (enable Gmail API, add redirect URI https://your-n8n.example.com/rest/oauth2-credential/callback, create OAuth client, sign in inside n8n).
2. n8n API key (Settings → API) for Data Table reads and writes from the Code node.
3. n8n Variables (or gmb-config.json for the build script):
   • GMB_WF_SEND_EMAIL_ID: set after WF02 is active
   • GMB_API_KEY: shared secret matching the Next.js app
   • N8N_BASE_URL: your n8n instance URL

3. Build phase one: the email sub-workflow#

Import WF02. Open gmbflow-02-send-review-email.json in n8n (Workflows → Import from file).

Connect Gmail. Open the Send Gmail node, select your Gmail OAuth2 credential, and confirm Email Type is html (static value, not an expression).

Activate and copy the ID. Activate the workflow, then copy its workflow ID into GMB_WF_SEND_EMAIL_ID (n8n Variable or gmb-config.json).

The sub-workflow accepts { to, subject, body, lead_id, business_id } from the gateway, waits on a staggered delay, sends via Gmail, then POSTs a lead.email_result callback so the gateway can flip the lead to sent or failed.

4. Build phase two: the API Gateway#

The source JSON is a template. The API Handler Code node contains the full CRUD logic but must be built with your table IDs embedded.

From the GMBFlow repo:

bun n8n/scripts/build-workflows.ts

This reads n8n/gmb-config.json and writes n8n/workflows/01-api-gateway.built.json with the handler code and CONFIG block inlined.

Import the built file. Import 01-api-gateway.built.json (not the source template), activate it, and note the webhook URL:

https://your-n8n.example.com/webhook/gmb-api

Every dashboard request is a POST with JSON { action, ...params } and header X-API-Key: your-gmb-api-key.

Key actions the gateway handles:

5. Configure the GMBFlow Next.js app#

Clone GMBFlow, copy .env.example to .env.local, and set:

N8N_WEBHOOK_URL=https://your-n8n.example.com/webhook/gmb-api
N8N_API_KEY=your-gmb-api-key
NEXT_PUBLIC_APP_URL=http://localhost:3000

Start the app:

bun dev

Open http://localhost:3000, create a workspace, and land on /b/{slug}.

Onboarding flow:

1. /onboard: three-step wizard (business name, Google place ID, owner email).
2. /b/{slug}/leads: add leads manually or import a CSV (name + email required; service and notes optional).
3. Assign a service to unassigned leads, then click Queue to trigger review emails.

Review page. Each queued lead gets a unique token. The email links to /review/{token}. On submit:

• 4-5 stars: rating saved, customer redirected to https://search.google.com/local/writereview?placeid=...
• 1-3 stars: rating and comment saved internally; no Google redirect

6. Import the workflow JSON#

Use the download buttons above in this order:

1. Bootstrap (gmbflow-00-bootstrap-tables.json): activate, run the webhook, copy table IDs.
2. Send Review Email (gmbflow-02-send-review-email.json): connect Gmail, activate, set GMB_WF_SEND_EMAIL_ID.
3. API Gateway: run build-workflows.ts in the GMBFlow repo, import the built JSON, activate.

Re-select credentials after every import. Update webhook URLs and API keys to match your instance, not the placeholder values in the shipped files.

Testing the workflow#

Validate each layer before queuing real customers:

1. Bootstrap idempotency. Run the bootstrap webhook twice. The second run should return existing tables without error.
2. Health check. POST to /webhook/gmb-api with { "action": "health" } and your X-API-Key header. Expect { "ok": true, "storage": "data-tables" }.
3. Create a business. Use the GMBFlow onboard wizard or POST { "action": "business.create", "slug": "test-co", "name": "Test Co", "place_id": "ChIJ..." }. Confirm three default services appear.
4. Queue one lead. Add a lead with a service assigned, queue it, and confirm the Gmail arrives with a working /review/{token} link.
5. Submit a low rating. Pick 2 stars on the review page. Confirm the rating appears in the dashboard but no Google redirect is offered.
6. Submit a high rating. Pick 5 stars. Confirm redirect to Google Business is offered and redirected_to_gmb is logged.
7. Duplicate guard. Try queuing the same lead again or re-submitting a review. Both should be blocked.

If emails fail with "Forbidden - perhaps check your credentials?", reconnect Gmail OAuth2 in n8n and confirm the Google Console redirect URI matches exactly.

Customization options#

• Email templates per service. Edit subjects and bodies in /b/{slug}/services. Use {{name}}, {{service}}, and {{review_link}} placeholders.
• Stagger rate. Change SECONDS_BETWEEN in the API Gateway Split Email Jobs Code node to tune Gmail batch spacing.
• Swap the sender. Any n8n email node (SMTP, SendGrid) can replace Gmail if you adjust WF02 accordingly.
• Add SMS or WhatsApp. Replace the email sub-workflow with a messaging channel; the gateway _emailJobs dispatch pattern stays the same.
• Multi-workspace. Each business is isolated by business_id. One n8n instance can serve many clients from the same three workflows.

Common mistakes that quietly break this#

• Importing the API Gateway source without building. The Code node is a placeholder until build-workflows.ts embeds your table IDs and API keys.
• Wrong import order. WF02 must be active before WF01, because the gateway calls the email sub-workflow by ID.
• Skipping the service assignment. Leads without a service_id are skipped at queue time. Assign a service before queuing.
• Gmail not connected on WF2. Queued emails fail silently until you select a real OAuth credential on the Send Gmail node.
• Mismatched API keys. The X-API-Key in the Next.js app, WF02 callback nodes, and the gateway CONFIG must all match.
• Re-queuing reviewed leads. The gateway blocks re-send for sent, opened, and reviewed statuses. Delete and re-create the lead if you truly need a second ask.
• Treating low ratings as public. The Google redirect only unlocks at 4+ stars on the review page. Never link customers directly to your Google review URL without the rating gate.

Conclusion#

You now have a complete Google review management stack: a branded dashboard for onboarding and lead management, three n8n workflows handling storage and email, and a review page that protects your public rating before unhappy customers ever reach Google. Happy customers get a one-tap path to your listing; unhappy ones give you private feedback you can act on. Duplicate guards, activity logs, and per-service email templates mean the system stays trustworthy as you scale past the first dozen leads.