Secure Invoice Ingestion with OpenAI, Slack & ERP Webhooks

Secure Invoice Ingestion with OpenAI, Slack & ERP Webhooks

Turn invoice PDFs into structured data automatically: this n8n workflow accepts documents via webhook, extracts invoice fields with OpenAI, auto-validates them, and posts approved invoices to your ERP—while sending any exceptions to Slack for human review before anything touches your system.

What this workflow does

• Receives invoice PDFs via a POST request to the /idp-ingest webhook, accepting the invoice as a binary file (or using body.fileContent where applicable).
• Validates intake by checking file type and size, and honoring an optional malware-scan status. It then creates correlation and document metadata for downstream processing.
• De-duplicates and routes outcomes using demo logic: duplicates and invalid intakes are routed to an exception path instead of being processed further.
• Extracts invoice data from PDFs by converting/reading PDF text and sending OCR text to OpenAI to return a structured invoice JSON.
• Validates invoice quality against a validation policy: required fields, non-negative amounts, presence of line items, and confidence thresholds.
• Auto-approves or escalates: valid invoices are approved; violations trigger an exception.
• Slack-based manual review for exceptions: the workflow posts a detailed message to Slack, waits for a reviewer’s webhook decision, and routes approved vs. rejected outcomes.
• Posts to your ERP for approved invoices via HTTP using an Idempotency-Key header, then generates a sanitized audit log. Rejected/duplicate items are closed without ERP posting.

Use cases

• Automate AP intake by converting invoice PDFs into ERP-ready JSON with OpenAI.
• Add a human-in-the-loop review step for low-confidence or invalid invoices using Slack.
• Prevent duplicate processing with idempotent ERP posting and correlation metadata.

Technical details

• n8n nodes/blocks: Webhook, Code, Switch, Wait, Slack, and supporting nodes (including Sticky Note for clarity).
• ERP integration: HTTP posting to an ERP endpoint with Idempotency-Key.
• Operational flow: exception handling via Slack + webhook-based reviewer decision.

Setup

Configure the /idp-ingest webhook in your source system to send a document binary file (or provide body.fileContent for the included Convert to File step), and use the generated resume webhook URL for the reviewer decision.