Purchase Approval Routing with Postgres, Email & Webhook

Automated Purchase Approval Routing with Postgres + Email + Webhooks

This n8n workflow automatically receives purchase requests via webhook, evaluates them against spend tiers, department budget status, and vendor risk stored in Postgres, then either auto-approves, rejects, or runs a sequential email approval chain—with final notifications sent to the requester and an audit message posted to Slack.

What this workflow does

• Receives & validates requests: Accepts a purchase request via a POST webhook, validates required fields, and normalizes currency amounts to USD.
• Loads decision inputs from Postgres: Retrieves vendor risk/approval status, department budget and manager details, and the last 30 days of spend with the same vendor.
• Applies policy rules: Uses spend tiers (including cumulative 30-day vendor spend), budget limits, self-approval avoidance, and vendor risk checks to determine whether to approve, reject, or require specific approval levels.
• Creates a pending record: Saves the request as pending in Postgres and immediately responds to the webhook caller with the request ID, current status, and required approvers.
• Runs sequential approvals (if needed): Sends an approval email with approve/reject links, waits for responses, and continues the chain with reminders until completion or expiry.
• Finalizes & audits: On approval, records the decision in Postgres, generates a PO number, commits budget, emails the requester, and posts an audit notification to Slack.

Use cases

• Centralizing purchase order approval routing for SaaS teams with consistent spend-tier governance.
• Reducing bottlenecks by auto-approving low-risk requests and escalating higher-risk ones.
• Auditable approval trails for vendor spend and department budget usage over rolling 30-day windows.

Technical details

• Integrations: Postgres (vendors, departments, requests, audit logs), Email, Slack, and a Webhook endpoint.
• n8n nodes/logic used: if, set, code, wait, switch, webhook.

Perfect for n8n users and automation engineers who need production-ready purchase approval workflows with Postgres-backed policy enforcement.