Automating Accounts Payable with n8n & UiPath

Modern SaaS world meets an ERP without an interface

Invoices arrived as PDF attachments, scans from the mailroom, and occasionally on paper. The real obstacle was the target system: an older ERP with no usable REST API, where every posting was typed manually into input masks. A pure OCR or workflow tool would have read the data but left the last mile into the legacy system unsolved.

The shared-service centre processed thousands of documents per month; every manual posting tied capacity needed for exceptions and closing work. An ERP migration was planned mid term but not affordable short term.

The goal was relief today that remains extensible tomorrow—without replacing the legacy system.

Double entry, lost cash discounts, missing audit trail

Finance re-checked amounts, vendors, and cost centres; deviations from the purchase order caused back-and-forth and delays. Cash discounts were lost because invoices were posted too late. At the same time, auditors needed a traceable trail: who approved up to which amount, and when did each document reach the ERP?

Approvals ran via email and Excel lists—with no central status per invoice. For audit questions, staff searched inboxes and network drives.

Vendor master data often differed slightly between OCR result and ERP—enough for manual rework on every other invoice.

Hybrid architecture as a deliberate choice

OCR vendors and collaboration tools offered APIs; the ERP did not. RPA alone would not elegantly connect email, AI, and approval. A pure n8n approach failed at the posting screen.

IT leadership wanted a clear split: cloud orchestration for everything API-capable, robots only for the GUI gap—documented and maintainable.

n8n as the orchestration layer for the API world

An n8n workflow watches a central mailbox via IMAP trigger, splits off attachments, and sends PDFs to OCR and AI-assisted extraction. n8n validates IBAN and VAT IDs against vendor master data, detects duplicates, and routes anything unclear to an approval in Slack or Microsoft Teams. Only once the record is complete and approved does n8n hand it on.

The architecture follows our process automation and API integration services. AI-assisted extraction sits in artificial intelligence—always with human approval before posting.

“OCR alone is not enough—what matters is the chain to the posted line in the ERP without anyone typing twice.”

UiPath as the last mile into the legacy system

For the API-less ERP, a UiPath robot performs the guided entry: it logs in, navigates the posting screen, fills in the verified fields provided by n8n, and files the original PDF in the document management system. This creates an end-to-end chain without touching or expensively re-integrating the grown system.

The robot uses a queue, technical user, and screenshots on deviation. n8n receives success or error code—on failure the document lands in a manual queue instead of half-posted in the ERP.

We explain this split of roles in the RPA vs API integration comparison. Budgeting is supported by the automation cost calculator.

Approval, audit, and operating logic

Approvals run via Teams with amount limits and four-eyes principle; every step is recorded in the audit log. Queues, retry logic, and alerting on OCR or RPA failure are part of the architecture—not an afterthought.

Audit receives exportable logs: intake, extraction, approval, posting time, PDF filing. That meets GoBD-oriented requirements without paper folders.

Engineering from East Frisia

“We no longer lose cash discounts to process—at most to real exceptions we handle deliberately.”

Design and delivery were led by Groenewold IT Solutions in Leer/East Frisia: a joint process workshop, a tightly scoped pilot with a few vendors, then extensions for additional tax and edge cases. Similar hybrid projects appear in our automation references.

Less typing, faster cycle times

Most invoices flow through without manual double entry; finance focuses on true exceptions and approvals. Cash-discount deadlines are met more reliably because documents are posted promptly and traceably.

Cycle times from intake to posting dropped measurably; error rates from typos in the screen fell. The shared-service centre scaled volume without proportionally more headcount.

Reference for hybrid automation

The project shows how n8n and UiPath complement each other: n8n connects cloud, AI, and communication, UiPath operates systems without an interface. In mid-sized companies with grown IT landscapes, this bridge is often the real value contribution.

For wholesale and shared services, the pattern transfers: API-first where possible, RPA for ERP screens, audit-ready trail—Made in Germany.