Invoice Approval Workflow vs. Purchase Order Matching: A Comparison for UK SMEs

Invoice approval workflows focus on authorising payment for an invoice, typically after goods or services are received. Purchase order (PO) matching, conversely, verifies an invoice against a pre-approved purchase order and often a goods receipt, ensuring that what was ordered, received, and billed align. While both aim to control expenditure and prevent errors, PO matching offers a more proactive control by validating spend before it's incurred, making it ideal for managing recurring or significant procurement.

For UK SMEs and growing businesses, managing financial operations efficiently is crucial. Payment delays, manual errors, and a lack of spending visibility can quickly impact cash flow and profitability. Two key processes – invoice approval workflows and purchase order matching – offer different approaches to controlling expenditure and streamlining your accounts payable. Understanding their distinctions is key to choosing the right controls without over-engineering your finance function.

Here’s a comparison to help you decide which approach, or combination, is best suited for your business.

Feature	Invoice Approval Workflow	Purchase Order Matching
Primary Goal	Authorise payment for an invoice.	Verify invoice against pre-approved spend and receipt.
Control Point	Reactive: After invoice receipt.	Proactive: Before spend is committed (PO) and after receipt.
Key Benefit	Ensures expenses are reviewed and approved by responsible parties.	Prevents unauthorised spend, reduces invoice discrepancies, ensures receipt of goods/services.
Typical Use Case	One-off purchases, services, non-PO expenses, low-value items.	Recurring purchases, inventory, project-based spend, high-value items, supplier contracts.
Complexity	Simpler to implement, often based on spend limits or department.	More complex, requires PO creation, goods receipt, and 2-way or 3-way matching.
Error Reduction	Reduces errors from unapproved payments.	Significantly reduces overpayments, duplicate invoices, and payments for unreceived goods.
Setup Effort	Lower: Define approvers, limits, and routes.	Higher: Requires PO system, receipt process, and matching rules.
Speed of Processing	Can be quick if approvers are responsive.	Can be slower if matching discrepancies arise, but faster for clean matches.

Invoice Approval Workflow

An invoice approval workflow is a structured process for reviewing and authorising supplier invoices before payment. It typically involves routing an invoice through a series of designated approvers based on criteria such as the invoice amount, department, or cost centre. The core purpose is to ensure that all expenses are legitimate, correctly coded, and approved by the appropriate personnel.

How it Works

Upon receipt, an invoice is entered into a system (manual or automated). It is then assigned to an approver, who reviews the details, confirms the goods or services were received, and authorises payment. If the invoice exceeds a certain threshold, it might require multiple approvals. Once approved, it proceeds to payment processing.

When it Breaks Down

• Manual Routing: Physical invoices or email attachments can get lost, leading to delays and missed payments.
• Approval Bottlenecks: If approvers are unavailable or slow to respond, the entire payment cycle grinds to a halt.
• Lack of Context: Approvers may lack the full context of a purchase, leading to rubber-stamping or unnecessary queries.
• No Pre-Approval: It's a reactive control; the spend has already occurred, making it harder to dispute or prevent.

Purchase Order Matching

Purchase order (PO) matching is a more robust control mechanism that verifies an invoice against a pre-approved purchase order and, often, a goods receipt. This process ensures that what was ordered, what was received, and what was billed are all in agreement. It typically involves 2-way matching (invoice to PO) or 3-way matching (invoice to PO to goods receipt).

How it Works

1. Purchase Order Creation: A PO is created and approved internally for goods or services to be procured. This commits the company to a specific spend.
2. Goods/Services Receipt: Upon delivery, a goods receipt (GRN) or service acceptance record is created, confirming that items were received as ordered.
3. Invoice Matching: When the supplier invoice arrives, it is electronically matched against the corresponding PO and GRN.
4. Discrepancy Resolution: If there are discrepancies (e.g., price variance, quantity mismatch), the system flags them for investigation and resolution before payment.

When it Breaks Down

• Poor PO Compliance: If staff bypass the PO system, matching becomes impossible.
• Inaccurate Goods Receipts: Incorrect or delayed recording of received goods leads to matching failures.
• Supplier Inconsistencies: Suppliers issuing invoices that don't clearly reference PO numbers or have different line items can cause issues.
• System Complexity: Implementing and maintaining a robust PO system can be more complex than a simple invoice approval workflow.

Choosing the Right Control Model

The decision between an invoice approval workflow, PO matching, or a combination of both depends on several factors specific to your SME:

Supplier Volume and Diversity

• Low Volume, Diverse Suppliers (e.g., many one-off contractors): An invoice approval workflow might be sufficient. The overhead of creating POs for every single transaction could outweigh the benefits.
• High Volume, Recurring Suppliers (e.g., raw materials, office supplies): PO matching becomes highly valuable. It automates verification for predictable spend, reducing manual checks significantly.

Recurring vs. Non-Recurring Spend

• Predominantly Non-Recurring/Ad-hoc Spend: Invoice approval is often the practical choice. It focuses on authorising the actual expense.
• Significant Recurring Spend: PO matching provides proactive control, ensuring that recurring orders align with agreed terms and quantities.

Approval Complexity and Risk Tolerance

• Simple Approvals, Lower Risk: A basic invoice approval workflow can manage risk effectively.
• Complex Approvals, Higher Risk (e.g., large projects, inventory): PO matching provides an essential layer of control by verifying spend at multiple points (commitment, receipt, invoice).

Desired Speed and Error Reduction

• Prioritise Speed for Simple Invoices: A streamlined invoice approval process can be very fast.
• Prioritise Error Reduction and Proactive Control: PO matching excels here, catching discrepancies before payment and preventing unauthorised spend.

Practical Recommendation Framework

To avoid over-engineering your finance function, consider this framework:

1. Assess Your Current Pain Points: Are you experiencing frequent payment delays? Overpayments? Unauthorised spend? This will guide your priority.
2. Categorise Your Spend:
   • Category A (High Value, Recurring, Strategic): Implement 3-way PO matching. This includes inventory, major project costs, and significant supplier contracts.
   • Category B (Medium Value, Recurring/Semi-Recurring): Implement 2-way PO matching. This might cover office supplies, software subscriptions, or regular services.
   • Category C (Low Value, Ad-Hoc, Services): Utilise an invoice approval workflow. This covers one-off consultancy, minor repairs, or incidental expenses.
3. Start Simple, Then Scale: Begin by automating your most problematic or highest-volume category. For instance, if inventory management is a mess, start with 3-way matching for those suppliers.
4. Leverage Automation Tools: Modern accounting software and dedicated procure-to-pay platforms can automate both invoice approval workflows and PO matching, reducing manual effort significantly.
5. Review and Refine: Periodically review the effectiveness of your chosen processes. Are they achieving the desired outcomes? Are there new bottlenecks?

For many growing UK SMEs, a hybrid approach often provides the best balance of control and efficiency. Implementing PO matching for your core, recurring spend, while maintaining a flexible invoice approval workflow for ad-hoc or service-based invoices, can dramatically improve financial control without creating unnecessary administrative burden.

If your business is struggling with stuck workflows, payment delays, or a lack of visibility in your finance operations, Bridgr Labs can help diagnose the issues and implement tailored solutions. Learn more about our approach to operational excellence on our FAQ page or explore further insights on our Insights page.

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Frequently asked questions

When is an invoice approval workflow sufficient on its own?

An invoice approval workflow is often sufficient for businesses with low transaction volumes, non-recurring expenses, or when the primary concern is simply ensuring that an expense is authorised before payment. It's suitable for services or one-off purchases where a formal purchase order isn't practical or necessary.

When should we implement purchase order matching?

Purchase order matching is best implemented when you have recurring purchases, significant spend with specific suppliers, or a need for tighter control over committed expenditure. It's particularly valuable for managing inventory, project costs, or any scenario where pre-approving spend and verifying delivery are critical.

Can we use both an invoice approval workflow and purchase order matching?

Yes, using both an invoice approval workflow and purchase order matching provides the most robust financial control. PO matching verifies that an invoice aligns with a pre-approved commitment, while an invoice approval workflow ensures the final payment is authorised, often by a different individual or department, adding an extra layer of scrutiny.

What's the primary benefit of automating these processes for an SME?

The primary benefit of automating these processes for an SME is a significant reduction in manual effort, leading to fewer errors, faster payment cycles, and better cash flow management. Automation frees up staff from repetitive tasks, allowing them to focus on more strategic activities and providing clearer visibility into spending.