Route AI-scored approval requests with GPT-4o-mini, Supabase and Gmail

Description

Quick overview
This workflow collects approval requests via an n8n form, uses OpenAI (GPT-4o-mini) to summarize and score risk, stores the request in Supabase, emails the right approver via Gmail with approve/reject links, then updates the Supabase record and notifies the requester by email.

How it works
Receives a new approval submission from an n8n form with request details like type, title, amount, department, justification, and requester email.
Sends the request data to OpenAI (GPT-4o-mini) to generate a short summary plus a risk score, priority, and suggested approval level.
Chooses an approver email and approval level based on amount thresholds and the AI risk score, then combines the AI output with the original form data.
Creates a new row in the Supabase approval_requests table with the request details, AI fields, and a generated request ID set to pending.
Builds approve/reject URLs that point to a webhook and emails the approver via Gmail with the request summary and one-click action links.
Accepts the approver’s click on the approval webhook, updates the matching Supabase record to approved or rejected with audit details, and emails the requester the final outcome via Gmail.

Setup
Add OpenAI API credentials and ensure the model selection (gpt-4o-mini) is available in your OpenAI account.
Add a Supabase credential and create an approval_requests table with columns that match the fields written by the workflow (for example request_id, status, approver_email, approval_level, ai_summary, risk_score, and priority).
Add a Gmail OAuth credential for sending emails to approvers and requesters.
Update the webhook base URL used in the approve/reject links to your n8n instance URL and ensure the approve-action webhook path is reachable from email recipients.
Replace the hardcoded approver email addresses (manager/finance_head/director) with real inboxes for your organization.

Additional info
How To Customize Nodes

Easy Changes

Form fields: Edit "New Approval Request Form" → add/remove fields
AI rules: Modify prompt in "Analyze Risk Priority" node
Amount thresholds: Update expressions in "Prepare AI Form Data"
Approver emails: Change ternary logic in approver_email field
Email templates: Edit HTML in Gmail nodes

Advanced Customization

Add Slack/Teams: Replace Gmail nodes
Multi-approver: Add sequential webhooks
Custom fields: Extend Supabase schema + form
Reporting: Add cron trigger for dashboard data

Add-ons

Immediate Extensions You Can Try

Telegram notifications** (parallel to Gmail)
Slack channels** per department
Sequential approvals** (Manager → Director)
PDF generation** of approved requests
Weekly reports** to finance team

Enterprise Features You Can Consider

Role-based access via n8n RBAC
Multi-tenant (separate Supabase schemas)
Custom branding on forms/emails
Integration with HRIS/Payroll systems

Use Case Examples

Purchase Orders:** Laptops, software licenses, office supplies
Expense Approvals:** Travel, client dinners, training courses
Document Sign-off:** Contracts, proposals, policy updates
Internal Requests:** Vacation, equipment, remote work setup
Vendor Onboarding:** New suppliers, service contracts
Budget Reallocation:** Department transfers, project funding
Overtime Authorization:** Weekend work, emergency coverage

Troubleshooting Guide

| Issue | Possible Cause | Solution |
| :-- | :-- | :-- |
| Form not submitting | Workflow inactive | Activate workflow, use Production URL |
| AI returns plain text | Markdown parsing failed | Check "Extract AI JSON Response" code |
| Webhook 404 error | Test URL used | Activate workflow, copy Production webhook URL |
| Email not sending | Invalid OAuth2 | Reconnect Gmail credentials |
| Supabase insert fails | Missing table/columns | Run schema SQL exactly as provided |
| "Requester Email Valid?" skips | Empty requested_email_by | Fill email field in form |
| Wrong approver | Amount thresholds | Verify logic in "Prepare AI Form Data" |

Need Help?

Our n8n workflow developers at WeblineIndia can help you with:

Custom approval workflows (multi-stage, conditional routing)
Enterprise integrations (ERP, HRIS, accounting)
White-label form builders
Performance optimization for 10K+ daily requests