n8n Expense Approval Workflow: Gmail & HTTP Webhook Routing

Automatically route expense approvals with an n8n webhook, Gmail, and HTTP updates

This n8n Expense Approval Workflow receives expense requests via an HTTP POST webhook, validates and routes them by amount for auto-approval or Gmail-based manager/director decisions, then records the final outcome to an external HTTP system and emails the requester with the result.

What this workflow does

• Receives an expense request through a webhook (HTTP POST) to the path expense-request.
• Normalizes & validates the incoming payload, assigning defaults such as request ID, currency, and approver emails when needed.
• Rejects invalid submissions with a validation reason, or routes valid requests by amount to one of the approval stages: auto-approval, manager approval, or director approval.
• Sends approval/notification emails using Gmail and waits for the manager/director to approve or decline within the configured time limit.
• Builds a final decision record including approved/rejected status, stage, approver, and reason.
• Posts the decision to your external system of record via an HTTP request (e.g., update https://example.com/api/expenses/decisions to your real endpoint).
• Emails the requester the final status via Gmail and returns the decision record as the webhook response.

Use cases

• Expense intake from a custom app or form that submits requesterEmail, amount, category, and description.
• Automating spend approval chains by amount (auto-approve small expenses; require manager/director for larger ones).
• Keeping a single source of truth by logging every decision to an external HTTP API.

Technical details

• Webhook (HTTP POST): listens on path expense-request.
• Nodes used: if, set, code, switch, gmail, webhook.
• Gmail OAuth2 credential required for sending approval and notification emails.
• Configurable default managerEmail and directorEmail (or provided per request).