How to identify duplicate invoices: Causes and prevention

Even well-managed finance teams can encounter duplicate invoices. A vendor might resend an unpaid invoice, or an AP clerk might re-enter one by mistake. In some cases, the duplication may point to something more deliberate, such as fraud.

Regardless of the cause, duplicate invoices introduce unnecessary cost, delay approvals, and increase the risk of financial reporting errors. Left unaddressed, they can lead to overpayments, reconciliation issues, and vendor friction.

Let’s walk through why duplicate invoices happen, how to identify them, and what businesses can do to prevent them.

What are duplicate invoices?

They may match exactly—same invoice number, vendor, and amount—or contain slight variations, such as a different date or a small formatting change. Some duplicates are unintentional, caused by manual entry errors or system issues. Others may indicate deeper problems, including fraud. In either case, they introduce unnecessary risk into the AP process.

Why duplicate invoices are an issue

Duplicate invoices often start as simple mistakes, but their impact can be significant if left unresolved:

• Overpayments: Paying the same invoice twice results in cash loss and recovery efforts
• Cash flow disruption: Duplicate payments temporarily reduce available working capital
• Reconciliation challenges: Extra entries complicate month-end close and financial reporting
• Audit and compliance exposure: Patterns of duplicate payments can signal weak controls
• Manual rework: Teams lose time investigating discrepancies and coordinating refunds
• Vendor tension: Overpaying and requesting reimbursement can erode trust

Even when caught, duplicates consume time and resources—and repeated issues can undermine internal credibility and vendor relationships.

Common reasons duplicate invoices occur

Duplicate invoices can result from honest mistakes or intentional fraud. The challenge is distinguishing between the two—and putting controls in place to catch both.

Non-fraudulent causes

Most duplicate invoices stem from routine errors in manual entry or system processing. Common scenarios include:

• Manual data entry: An invoice is keyed in twice by mistake—often because it was unclear whether it had already been entered
• Vendor resubmissions: If a vendor doesn’t receive payment on time, they may resend the invoice. Without a tracking system, both versions can be processed
• System limitations: AP automation tools may miss near-duplicates if OCR misreads details—such as interpreting an “8” as a “B”
• PO corrections: An invoice may be resubmitted with a revised purchase order number, while all other fields remain unchanged

These cases are rarely intentional, but they can still lead to overpayments, accounting discrepancies, and vendor confusion if not flagged early.

Fraudulent tactics

Unlike system or human error, fraudulent duplicates are intentional. They often rely on small changes or timing to bypass internal checks.

• Slight variations: The same invoice is resubmitted with a minor edit—such as a new date or invoice number—to avoid detection.
• Ghost vendors: A fake vendor profile is created to submit false invoices under thresholds that don’t require multiple approvals.
• Invoice splitting: A high-value invoice is divided into smaller ones to sidestep higher approval requirements.
• Timing attacks: Fraudulent invoices are submitted during high-volume periods, such as month-end close, when oversight is more likely to slip.

These tactics often succeed because they resemble legitimate transactions while exploiting gaps in process and validation.

How to distinguish between error and fraud

Determining whether a duplicate invoice is a simple oversight or a deliberate act isn’t always straightforward. But certain patterns can help you assess intent and decide which cases warrant closer scrutiny.

No single factor confirms intent—but together, these signals can help prioritize which entries deserve further review.

Best practices for preventing duplicate invoices

Even with the best tools, preventing duplicates starts with process discipline. These foundational practices help reduce both accidental errors and opportunities for accounts payable fraud.

• Centralize invoice intake: Route all invoices—regardless of format—through a single platform or intake team. This avoids duplicates from multi-channel submissions
• Standardize formatting: Encourage vendors to follow a consistent format for invoice numbers, dates, amounts, and PO references. Structured data makes validation easier
• Enforce validation checks: Before payment, confirm invoice details against vendor records, purchase orders, and past payments. Even a basic review can prevent common errors
• Minimize manual input: Reduce manual data entry by using automation to capture invoice fields. Fewer touchpoints mean fewer chances for duplication
• Conduct regular audits: Set a monthly or quarterly cadence to review invoice activity, surface patterns, and flag irregularities that daily workflows may miss

These steps create multiple layers of protection—helping teams catch errors early and limit exposure to fraud before payments are processed.

How technology helps prevent duplicate invoices

Modern AP tools go beyond speeding up payments—they offer built-in controls that help identify and prevent duplicate invoices before they become costly. Here’s how businesses use technology to reduce risk at scale:

1. Automated duplicate detection

Most ERP and AP automation systems include rules that detect identical or highly similar invoices before they reach the payment stage.

For example, an invoice labeled “INV-1024” might be flagged if a similar one labeled “INV-1024A” was already paid. These alerts prevent accidental overpayments and create a second checkpoint before funds leave the business.

2. Invoice data extraction and validation

OCR-enabled tools digitize invoice details and match them against purchase orders, vendor records, and past transactions. This reduces manual entry and helps catch discrepancies—such as mismatched POs or repeated invoice numbers—early in the process.

3. Risk scoring with AI and machine learning

AI-powered platforms analyze historical payment behavior and assign risk scores to new invoices. These systems can detect patterns—like duplicate amounts with altered dates or minor vendor name changes—and surface invoices that warrant closer inspection.

4. Approval workflow controls

Platforms like NetSuite, SAP, and Microsoft Dynamics allow for layered approval workflows. These workflows prevent invoices from being paid before appropriate review, especially when thresholds are exceeded or duplicate behavior is suspected.

Technology adds multiple checkpoints across the invoice lifecycle—helping teams catch errors early while reducing reliance on manual oversight.

How to resolve duplicate invoices

Even with controls in place, duplicates can still occur. When they do, taking swift, structured action minimizes disruption and maintains vendor trust:

• Verify the issue: Confirm whether the invoices are exact or near-duplicates. Check submission dates, invoice numbers, payment records, and supporting documents
• Gather documentation: Collect relevant purchase orders, receipts, communications, and prior payment confirmations to understand the full context
• Log the incident: Record the duplicate in your AP or ERP system for audit purposes. If the cause stems from a system or process gap, flag it for internal review
• Tag or restrict the vendor: Use platform tags, alerts, or approval rules to prevent the same vendor or invoice number from being processed again without additional checks

How to communicate with vendors and recover funds

If a duplicate payment is made, a clear and professional response helps maintain the vendor relationship while resolving the issue efficiently:

• Reach out promptly with a summary of the duplicate and supporting documentation
• Request a refund or credit memo in line with your internal policy and vendor terms
• Record the resolution in your system, and update vendor notes or payment workflows to avoid recurrence

Vendors are often cooperative when the issue is handled transparently. A documented resolution process ensures accountability—and helps your team learn from each incident.

Stop duplicate invoices before they start

Duplicate invoices don’t just happen—they slip through when AP processes are slow, manual, or disconnected. Ramp helps you reduce that risk by streamlining invoice intake, automating reviews, and keeping everything in sync from the start.

With Ramp, you can:

• Automate invoice processing: Use AI-powered OCR to extract invoice details, apply suggested GL codes, and reduce manual errors for clean, audit-ready records
• Simplify approvals with built-in workflows: Route invoices to the right stakeholders with layered rules, automated reminders, and real-time status tracking
• Sync with your accounting tools: Connect with QuickBooks, Xero, NetSuite, and more to keep records accurate and avoid double entries across systems

By the time a payment goes out, you’ve already caught the mistakes, flagged the duplicates, and finalized everything in one place.

Let’s simplify your AP process. Try Ramp invoice management software or explore a hands-on demo to see it for yourself.