n8n Purchase Requisition Approvals: Google Sheets + Gmail

Route Purchase Requisition Approvals with n8n Forms, Google Sheets Budget Checks, and Gmail

This n8n workflow automatically collects purchase requisitions, validates cost center budgets in Google Sheets, and sends approval/rejection requests via Gmail—then logs outcomes back to Google Sheets.

What this workflow does

• Receives submissions from an n8n form for a purchase requisition.
• Standardizes and validates data: it generates a requisition ID, calculates the estimated total cost, and rejects requests with missing/invalid required data.
• Checks cost center status in Google Sheets by looking up the selected cost center and rejecting the requisition if the cost center is not Active.
• Enforces budget availability: compares the requisition total against the cost center’s available budget from Google Sheets and rejects if funds are insufficient.
• Determines approval level using configured spend thresholds, then selects the appropriate approver email.
• Sends approval requests via Gmail with approve/reject links, and waits for the approver’s decision.
• Logs results: if rejected, it logs the rejection to Google Sheets and emails the employee the outcome; if approved, it updates the cost center’s used/available budget, appends the requisition to a requisition log sheet, and emails an approval confirmation.

Use cases

• Organizations that need purchase requisition approvals with spend-based routing (e.g., managers approve small requests; executives approve larger ones).
• Teams that want budget guardrails enforced automatically using a Google Sheets cost center budget ledger.
• Companies standardizing workflows where every requisition must be tracked with an ID and logged approvals/rejections.

Technical details

• Integrations: Google Sheets and Gmail
• n8n nodes used: if, set, code, wait, gmail, sticky note
• Setup requirements: connect Google Sheets credentials and provide the Google Sheets document ID and sheet/tab IDs for Budget_Master and Requisition_Log (as configured in the workflow).