Detecting discrepancies in supplier invoices: the six most common errors

These are the key points

• Supplier invoice discrepancies at MSPs are almost always small per invoice line but large in scale across the customer base.
• There are six recognisable discrepancy types: price discrepancies, volume errors, services still running after cancellation, duplicate billing, unprocessed changes and rate changes without an update.
• Manual detection finds a discrepancy weeks later on average, sometimes only after the customer invoice has already been sent.
• Automatic detection flags a discrepancy the moment the purchase invoice arrives, always before pass-through billing.
• ResalePartners detects discrepancies automatically by comparing against more than 110 supplier integrations.

Why supplier invoice discrepancies stay unnoticed for so long

Supplier invoices for MSPs and telecom resellers are not simple. You receive invoices from various suppliers, each with its own invoice structure, its own rate models and its own rhythm. With one supplier the information sits in a detailed CSV export, with another in a PDF of a hundred lines. Some invoices use fixed subscriptions, others variable usage. That makes manual comparison fundamentally unmanageable.

On top of that, back-office staff are not looking for discrepancies: they process invoices. If an invoice looks the way it always does, it gets posted. A rate change a supplier made three months ago but that is small in size simply does not stand out. Certainly not when you go through hundreds of invoice lines every month.

The result is a structural gap between the moment a discrepancy arises and the moment you discover it. That gap is several weeks on average, sometimes months. And in the meantime, customer invoices are sent based on incorrect purchasing data. That costs margin, causes disputes and undermines confidence in your administration.

The six most common discrepancy types in supplier invoices

Based on the practice of MSPs and telecom resellers, there are six discrepancy types that occur by far the most often and cause the most financial damage when they go unnoticed.

1. Price discrepancy: a different rate than agreed

The supplier has adjusted its rates, but you did not notice. Or there has been a contract renewal in which a discount agreement lapsed. Or a mistake was made when implementing a new pricing agreement. The result: the purchase invoice contains a rate that differs from what is entered in your system. With this type of discrepancy the difference per invoice line is often small, but multiplied across all customers and all months it adds up quickly.

2. Volume error: different quantities than expected

This is particularly relevant for telecom resellers. A customer has agreed a certain call volume. The supplier invoice shows higher usage, or in fact lower. That can mean a customer has called outside the bundle and you have to process those extra costs. Or that the customer has scaled back their usage but the supplier still billed the old volume. Without comparison against the expected volumes, you do not see this.

3. Service still running after cancellation

A customer cancels a service. You process it in the PSA. But at the supplier the service is not ended on time, or the cancellation was submitted but not processed. The next month that service is simply back on the invoice. This is one of the most costly discrepancies because, by definition, it repeats until someone notices it. A month after cancellation you are still paying, two months, sometimes longer. And those costs are rarely reclaimed.

4. Duplicate billing

The same service or the same invoice number appears twice. This can happen because a supplier sends a correction invoice that was communicated unclearly, or because an invoice came in through two channels. In manual processes, duplicate billing is not always recognised, certainly not when the invoice numbers or the layout differ slightly. Automatic systems recognise identical or near-identical items immediately.

5. Unprocessed change

A customer adds a Microsoft 365 licence. That change is in the PSA. But has that extra licence also been processed as extra purchasing for that customer? And is the corresponding sales entry ready? If the link between order, purchasing and customer profile is not maintained automatically, a gap appears. The change has been made, but the financial processing lags behind. This is a subtle but common type of discrepancy.

6. Rate change not passed through to the sale price

The purchase price has risen but the sale price has not been adjusted. Technically this is not an invoice discrepancy: the supplier is billing correctly. But the result is a margin that shrinks without you seeing it. This type of "hidden discrepancy" only becomes visible when you place purchasing and sales side by side consistently, by service and by customer. Without that comparison, your sales team applies a price that is too low for months on end.

What does an unnoticed discrepancy cost in practice?

The financial damage of an undetected discrepancy depends on two factors: the size per invoice line and the number of customers the discrepancy affects. It is precisely that combination that makes discrepancies so dangerous in the MSP context.

Take a rate change of fifty cents per month per user. On one customer with ten users that is five euros per month. On fifty customers with twenty users on average that is a thousand euros per month, twelve thousand euros per year. That is damage charged directly against the margin, structurally and without ever appearing in a report as long as the discrepancy goes unnoticed.

On top of that comes the timing gap. Manual checking detects a discrepancy on average only after the customer invoice has already been sent, sometimes only after the month-end close. That means you have to send out a credit note, have a discussion with the customer and go through a correction round. That burden is not only financial but also operational, and it harms confidence in your administration.

Automatic detection prevents all that damage by flagging the discrepancy the moment the purchase invoice arrives, before it is passed on to the customer. No credit notes, no disputes, no correction work.

How does automatic discrepancy detection work?

With InkoopControle from ResalePartners every incoming supplier invoice is automatically compared with the known purchasing per customer. That comparison process runs on three levels at once.

First, the rate is checked: does the billed rate match the contract agreement and the entered purchase price per service? Second, the volume is checked: does the billed number of units, users or usage volume match what is expected based on active services and subscriptions? Third, the service delivery itself is checked: are there invoice lines for services that have already been cancelled, or are lines missing for services that are in fact active?

Every discrepancy is presented immediately as an alert. Only once all discrepancies have been reviewed and approved can billing proceed towards the customer. The system works with more than 110 supplier integrations, from telecom suppliers such as Dstny, Gamma and RoutIT to software suppliers such as Microsoft 365 and platforms such as Pax8 and Ingram Micro. Want to know how automated invoice processing lays the foundation for discrepancy detection? Or how you connect purchasing costs per customer to assign discrepancies straight to the right customer?

What do you do when you have found a discrepancy?

When a discrepancy is flagged automatically, there are three steps. First, you assess the discrepancy: is it an error at the supplier, a change you have not yet processed, or a new situation that needs to be implemented? Second, based on that assessment you decide whether to contact the supplier for a credit note or correction, or to process the discrepancy internally. Third, you document the action so the discrepancy remains traceable for any audits or customer discussions.

The advantage of automated detection is that you carry out this process before there is any financial damage. The discrepancy does not come via a complaining customer or the month-end close: it comes via an alert at the moment of invoice processing. That puts you in control. You act on facts and with time to resolve the situation properly. Want to find out how monitoring purchasing as an MSP relates to discrepancy detection? And how purchasing control works more broadly as a foundation for margin management?

Want to see which discrepancies are sitting in your supplier invoices?

Book a free demo of InkoopControle and discover in 30 minutes how automatic discrepancy detection works for your specific supplier mix. Bring along a few purchase invoices and show us how things work for you now: we will show you how they can be done better.

View the full purchasing control for MSPs