{"product_id":"n8n-invoice-approval-automation-gpt-4o-google-sheets","title":"n8n Invoice Approval Automation: GPT-4o + Google Sheets","description":"\u003ch3\u003eAutomatically approve invoices from PDF submissions—powered by GPT-4o, Google Sheets, and Gmail\u003c\/h3\u003e\n\u003cp\u003eThis n8n workflow receives invoice PDFs via a webhook, extracts and validates invoice data using OpenAI (GPT-4o), checks for duplicates in Google Sheets, and routes each invoice for automatic or manual approval—while notifying vendors and finance via Gmail.\u003c\/p\u003e\n\n\u003ch3\u003eWhat this workflow does\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eReceives invoices via POST webhook\u003c\/strong\u003e including vendor details and the PDF file.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eExtracts structured invoice fields\u003c\/strong\u003e by pulling text from the PDF and using OpenAI to convert it into amounts, dates, line items, and payment information.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eNormalizes and validates required fields\u003c\/strong\u003e; if key fields are missing, it emails the vendor through Gmail.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eDetects duplicates in Google Sheets\u003c\/strong\u003e by searching for an existing invoice with the same invoice number. Duplicates are flagged and finance is notified by email.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eAnalyzes categorization, priority, and approval need\u003c\/strong\u003e using OpenAI, including a check that the total matches \u003cem\u003esubtotal + tax\u003c\/em\u003e.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eAuto-approves or requests approval\u003c\/strong\u003e: low-value, low-risk invoices are auto-approved; others trigger an approval request and wait for a decision submitted via webhook.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eWrites results back to Google Sheets\u003c\/strong\u003e with the final approval status and sends a completion notice to the finance team via Gmail.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eUse cases\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003eFinance teams that want \u003cstrong\u003einvoice approval automation\u003c\/strong\u003e without manually copying PDF data.\u003c\/li\u003e\n  \u003cli\u003eSaaS operators needing \u003cstrong\u003eduplicate invoice prevention\u003c\/strong\u003e using Google Sheets as the source of truth.\u003c\/li\u003e\n  \u003cli\u003eOperations workflows where vendors must be contacted automatically when invoice fields are incomplete.\u003c\/li\u003e\n  \u003cli\u003eTeams that require a \u003cstrong\u003ehuman-in-the-loop approval\u003c\/strong\u003e flow based on GPT-4o risk\/priority assessment.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eTechnical details\u003c\/h3\u003e\n\u003cul\u003e\n  \u003cli\u003eIntegrations\/credentials: \u003cstrong\u003eOpenAI\u003c\/strong\u003e (two AI steps: extraction + analysis), \u003cstrong\u003eGmail\u003c\/strong\u003e (vendor, approver, finance, admin notifications), and \u003cstrong\u003eGoogle Sheets\u003c\/strong\u003e (duplicate checks + final record writing).\u003c\/li\u003e\n  \u003cli\u003eKey workflow nodes: \u003cstrong\u003eif\u003c\/strong\u003e, \u003cstrong\u003eset\u003c\/strong\u003e, \u003cstrong\u003ecode\u003c\/strong\u003e, \u003cstrong\u003ewait\u003c\/strong\u003e, \u003cstrong\u003egmail\u003c\/strong\u003e, \u003cstrong\u003eswitch\u003c\/strong\u003e.\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"N8N Commerce","offers":[{"title":"Default Title","offer_id":46066367004851,"sku":"N8N-19739","price":4.99,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0749\/6279\/6723\/files\/fzGBgUQUpvBqgQNYLGv-T_wM820ULE.png?v=1789895275","url":"https:\/\/buyflowscripts.com\/products\/n8n-invoice-approval-automation-gpt-4o-google-sheets","provider":"N8N Commerce","version":"1.0","type":"link"}