Invoice mistakes that delay a consultancy's fees

Why a client can hold back every payment over one small invoice error, what a consulting invoice must carry, and what to check before you chase.

By Achekam · 11 October 2026 · 5 min read · For Consulting businesses in South Africa, Nigeria, Kenya

The project was delivered on time, the client's managing director said the board pack was the best they had seen, and the invoice went out the same week. Sixty days later it is still unpaid. When someone finally phones, the answer is that the invoice quoted last year's order number and was addressed to the holding company instead of the operating subsidiary. Nobody told you. It has been sitting in a query folder ever since.

For a consultancy, this is one of the most frustrating ways to lose cash: the work is done and accepted, and the money stalls over a detail on a piece of paper. The fix is mostly in how the invoice is prepared and sent, not in how hard you chase.

One small error can freeze the whole account

ACCA stresses that invoices must be sent quickly and accurately, because an inaccurate invoice can let a customer claim a dispute and stop paying all invoices until it is resolved. That last part is the dangerous one. A single wrong invoice can give a client's accounts department a reason to hold back payment of every invoice on your account, including the ones that were right.

ICAEW adds a quieter point that every consultancy should take to heart: a customer will not necessarily say it is withholding payment because something was wrong with the invoice. In a large organisation a query can sit in a queue, and the person who could fix it in a minute may never hear about it.

What a consulting invoice must carry to be paid

Clients' payables teams match invoices to something: an order, a contract, an approval. If they cannot match yours, it waits. Before issuing, check that the invoice shows:

• The correct legal entity as the customer, with its registered name and address, not the trading name or the group parent.
• The client's order or contract reference, where the client issues one. Some clients will not process an invoice without it.
• What the fee is for, in words the approver will recognise: the engagement name, the phase or milestone, and the period covered.
• The agreed rate or fixed amount, exactly as in the engagement letter, with any expenses listed separately.
• Your VAT registration number and the words "Tax Invoice" if you are registered for VAT, so the client can claim its input tax where its rules allow.
• Payment details: bank account, reference to use and the due date.

ACCA's description of good credit control starts long before chasing. It includes screening who gets credit, agreeing the terms of credit in advance, including the credit limit, credit period, discounts and interest, issuing accurate invoices quickly, and collecting overdue accounts systematically, fairly and within the law. ACCA also notes that customers generally will not pay until they receive the invoice, so a delay in invoicing becomes a delay in payment. For the terms side, see the essentials of a credit policy.

Send it promptly, to the person who pays

The project sponsor approves the work. Someone else pays for it. Send each invoice:

1. within days of the milestone or month end, not when the partner has time;
2. to the accounts payable address the client gave you, with the sponsor copied if they must approve;
3. as a PDF the client can file, not as a link they must log in to see.

Ask at the start of every engagement who receives invoices, what reference they need and how many days their approval cycle takes. Write the answers on the engagement file.

Check before you chase

ICAEW's helpsheet on chasing debtors advises that before chasing a customer for payment, a business should check that its invoice is correct, includes all the details needed for payment, was sent to the right person and was received.

Turn that into a short routine before the first reminder on any overdue invoice:

• Re-read the invoice against the engagement letter and the client's order.
• Confirm the address it went to, and whether the send was successful.
• Ask the client, plainly, whether anything on the invoice is stopping payment.

The third question can surface the problem in one call. A chase that opens with an accusation, when the error was yours, damages a relationship you have spent months building.

Issuing, e-mailing and adding a pay link in Achekam

In Achekam, a customer invoice starts as a draft you can change or delete. That is the moment to check it against the list above, because issuing it takes the next number in the sequence and posts it to the ledger as debtors, sales and output VAT. The sale is in the books the moment the invoice is issued, with no separate step to transfer it.

A few details help with the accuracy problems described here:

• VAT number and title. You enter your VAT registration number in Settings under Firm Profile. Documents made by the server print it, and are titled Tax Invoice only when a VAT number is set. A VAT-registered consultancy that forgets this step sends invoices without the title its clients' payables teams look for.
• PDF and e-mail. An issued invoice can be downloaded as a PDF on your letterhead and e-mailed from the invoice, with or without a pay link. A failed send is reported as not sent, so you know before you chase that the client may never have received it.
• A pay link. You can create a payment link for an issued invoice, copy it or e-mail it with the invoice, and the client pays on a public page showing your business's name and branding. There is no link for draft or voided invoices. A link lasts 14 days by default, and the business can set it anywhere from 1 to 720 hours. An open link for the same amount is reused rather than duplicated.

When a client pays through the link and the gateway verifies the payment, Achekam records it as a receipt against the invoice, debiting that gateway's clearing account and crediting trade receivables, and the invoice shows as paid or part-paid. The amount is checked against what the link asked for, and a repeated notification never pays twice.

If fee income is healthy but cash still is not, profit but no cash looks at the wider causes. Before the next invoice run, take the three clients who paid slowest last quarter and ask each one what their payables team needs to see on your invoice.

General guidance only, not advice on your own circumstances. Tax and payroll rules change: check the current position with the authority or your adviser.