Automate Invoice Data Extraction with n8n & LlamaParse

1. The Invoice Processing Nightmare for Sarah

Imagine Sarah, an accounts payable specialist at a mid-sized company. Every day, her inbox overflows with PDF invoices, mostly from payment platforms like PayPal. Sarah’s job is to extract key information — invoice number, dates, supplier details, line items, VAT, and totals — to reconcile payments and update spreadsheets. It takes her at least 30 minutes per invoice. Multiply that by dozens or hundreds monthly, and the time wasted is staggering. Mistakes also creep in because manually copying data from PDFs is tedious. Sarah needs a reliable way to automate this invoicing task with precision and minimal manual effort.

2. What This Automation Does ⚙️

This unique n8n workflow streamlines Sarah’s invoice processing by automatically:

• Watching her Gmail inbox for new invoice emails from [email protected] with PDF attachments.
• Uploading invoice PDFs to the LlamaParse API, a powerful cloud-based PDF parsing service designed for complex documents including tables and embedded structures.
• Polling LlamaParse for parsing completion and, once ready, retrieving the invoice content in Markdown format.
• Feeding the Markdown content to OpenAI GPT-3.5 Turbo via the LangChain integration to extract structured invoice data like invoice date, supplier name/address, customer details, line items, prices, VAT, and totals.
• Appending the cleaned and structured data into a Google Sheet specifically configured as an Invoice Reconciliation Sheet.
• Marking the original email with the “invoice synced” Gmail label to avoid duplicate processing and aid quality control.

By automating this workflow, Sarah can save hours each week and drastically reduce human errors on invoice data entry.

3. Prerequisites ⚙️

• 📧 Gmail account with the label “invoice synced” created and OAuth2 credentials set up
• 🔐 LlamaIndex API access for LlamaParse PDF parsing service
• 🔑 OpenAI API credentials for GPT-3.5 Turbo model accessed via LangChain nodes
• 📊 Google Sheets account with a dedicated Invoice Reconciliation spreadsheet sharing the document ID and sheet name
• ⏱️ n8n account with access to the LangChain integration and ability to run workflows periodically
• Optional: Self-hosting n8n for cost control and data privacy (e.g., via Hostinger)

4. Step-by-Step Guide to Set Up the Workflow ✏️

Step 1: Configure Gmail Trigger to Watch Invoice Emails

In n8n, click + Add Node → Search and select Gmail Trigger. Configure it as follows:

• Filter emails with query: has:attachment sender:[email protected]
• Enable Download Attachments to ensure PDFs are available
• Set polling interval to every minute for near real-time processing

You should see the Gmail node waiting to trigger on incoming invoice emails.

Common mistake: Forgetting to create the “invoice synced” label ahead of time will cause duplication later.

Step 2: Split and Get Label Names From Incoming Emails

Add the Split Out node on the label IDs from Gmail, then Gmail Get operations to retrieve each label’s name and use an Aggregate node to combine them into a list. This helps to check if the email is already processed.

Step 3: Use ‘If’ Node to Filter Unprocessed PDF Invoices

Create an If node that checks two conditions:

• The attachment MIME type equals application/pdf
• The email labels do not include “invoice synced” (filters out previously processed emails)

If both conditions are met, the workflow proceeds. Otherwise, it stops here.

Step 4: Upload PDF to LlamaParse for Advanced Parsing

Add an HTTP Request node to upload the invoice PDF to the LlamaParse API endpoint: https://api.cloud.llamaindex.ai/api/parsing/upload. Configure:

• Method: POST
• Content Type: multipart-form-data
• Attach the PDF binary data with key file
• Authentication via HTTP Header Auth with your LlamaIndex API key

Once uploaded, you get a job ID from the response to check processing status.

Step 5: Poll LlamaParse to Check If Parsing Is Complete

Use an HTTP Request node to repeatedly query https://api.cloud.llamaindex.ai/api/parsing/job/{{jobId}} with your job ID from the upload. A Switch node routes the flow based on status: SUCCESS, PENDING, ERROR, or CANCELED.

If PENDING, a Wait node pauses for 1 minute before rechecking.

Step 6: Retrieve Parsed Invoice Data in Markdown Format

Once the job status is SUCCESS, fetch the Markdown result using another HTTP Request node targeting https://api.cloud.llamaindex.ai/api/parsing/job/{{jobId}}/result/markdown.

Step 7: Apply OpenAI LLM for Structured Data Extraction

Add the LangChain OpenAI Model node set to gpt-3.5-turbo-1106 with zero temperature for consistent results.

Feed the Markdown invoice data into the Chain LLM node with a prompt that instructs the AI to extract specific fields like invoice date, invoice number, purchase order number, supplier and customer details, VAT numbers, shipping addresses, line items with prices, and totals.

Use the Structured Output Parser node right after to validate and format the AI output as JSON matching your Google Sheets schema.

Step 8: Map and Append Extracted Data to Google Sheets

Add a Set node mapping the output JSON from the parser, then a Google Sheets node to append this data into your Invoice Reconciliation spreadsheet.

Ensure your document ID and sheet name are correctly set in the Google Sheets node.

Step 9: Label the Original Email as ‘invoice synced’

Finally, add a Gmail node configured to add the “invoice synced” label to the email message ID to mark it as processed.

This prevents duplicate workflows triggering on the same invoice again.

5. Customizations ✏️

• Change Invoice Sender Filter: In the Gmail Trigger node, modify the sender email from [email protected] to any other vendor email to track different sources of invoices.
• Add More Data Fields: Edit the JSON schema in the Structured Output Parser node by adding new fields such as payment terms or due dates for richer invoice analysis.
• Switch Output Storage: Replace the Google Sheets node with an Airtable or Excel integration if you prefer to store invoice data elsewhere.
• Adjust Polling Interval: In the Wait node, increase or decrease the 1-minute wait time for faster or more conservative API polling to balance API limits and responsiveness.
• Improve AI Model Settings: Change the OpenAI Model node temperature or try other GPT models for more creative or stricter data extraction based on your invoices.

6. Troubleshooting 🔧

Problem: “No PDF attachment found or wrong MIME type”

Cause: Emails don’t have invoice PDFs or attachments are not recognized as application/pdf.

Solution: Verify the Gmail filter query matches emails with PDFs. Check the attachment MIME type in the incoming data. Adjust filter logic in the If node accordingly.

Problem: “LlamaParse API returning ERROR or CANCELED status”

Cause: The uploaded PDF might be corrupted, unsupported, or API credentials misconfigured.

Solution: Test the PDF manually via LlamaCloud UI. Check API key validity and correct HTTP header authorization setup in the HTTP Request nodes.

Problem: “Google Sheets append operation fails”

Cause: Spreadsheet ID or Sheet name incorrect, or OAuth scopes missing.

Solution: Double-check the Google Sheets document ID and sheet name. Verify OAuth credentials have editing privileges.

7. Pre-Production Checklist ✅

• Confirm Gmail label “invoice synced” exists and OAuth2 is connected
• Verify LlamaIndex API credentials and test API connectivity
• Ensure OpenAI API token is valid and LangChain nodes are correctly configured
• Test Google Sheets access and write permissions
• Send test invoice email from [email protected] with PDF attachment to Gmail
• Run workflow manually to observe step-by-step execution and fix any errors

8. Deployment Guide

Once tested, activate the n8n workflow so it monitors your inbox continuously. The workflow runs every minute, processing new PDFs almost real-time. Monitor workflow execution logs in n8n for occasional errors or parsing failures. Consider setting up error notifications in n8n for timely awareness of issues.

9. FAQs

Can I use another email provider instead of Gmail?

Yes, but you’ll need to use an n8n node compatible with that provider and adapt the email filtering and label management accordingly.

Does this consume OpenAI API credits?

Yes, each invoice extracted uses API calls. Keep track of your OpenAI usage to manage costs.

Is the invoice data secure?

Your data travels through LlamaParse and OpenAI APIs. For sensitive workflows, consider self-hosting n8n and use encrypted API keys.

Can this handle large volumes of invoices?

Yes, but be mindful of API rate limits on LlamaIndex and OpenAI. Adjust polling intervals and optimize workflows as needed.

10. Conclusion

By following this detailed workflow, you will have automated the extraction of invoice data directly from email PDFs into Google Sheets, freeing Sarah from hours of manual data entry each week. This setup reduces errors, accelerates financial reconciliation, and brings a scalable solution to account payable processing.

Next, consider automating payment reminders based on invoice due dates, integrating with accounting software like QuickBooks, or extending to multi-vendor invoice processing by adjusting email filters.

Happy automating your invoicing process with n8n, LlamaParse, and OpenAI!