Guide
Seven invoice mistakes that delay payment.
Most late payments are not disputes. They are documents that a bookkeeper could not process and quietly pushed to the bottom of the pile.
What goes wrong
1. No ABN on the invoice
A tax invoice must show the supplier’s ABN. Without one, the business paying you may be required to withhold tax from the payment — so the invoice does not just get delayed, it gets paid short.
Check the number before you send it, too. A transposed digit fails the same way.
2. Calling it a tax invoice when you are not registered
Only a GST-registered business issues a tax invoice showing GST. If you are not registered, the heading is Invoice and there is no GST line. Getting this wrong means showing tax you had no right to collect.
3. Taking 10% off a GST-inclusive total
The GST inside a total is one eleventh, not one tenth. On a $1,000 invoice the wrong method is out by $9.09 — small enough to slip through, large enough to fail a reconciliation.
The arithmetic, with worked examples.
4. Rounding each line separately
Apply GST to the invoice total, not line by line. Rounding ten lines individually is how an invoice ends up a cent away from its own total, and a cent is enough for software to reject it.
5. No buyer details over $1,000
At $1,000 or more, the buyer must be identified by name or ABN. This is the most commonly missed requirement, because an invoice format that was fine for months crosses the threshold without anyone noticing.
6. Duplicate or missing invoice numbers
Numbers should be unique and sequential. Two invoices sharing a number means one of them cannot be entered, and you will not find out until someone chases the payment.
7. Vague descriptions
“Services rendered” tells the person approving it nothing. They cannot match it to a purchase order or a budget line, so it waits. Describe what was actually supplied, and when.
The cheapest fix
All seven are structural, not judgement calls. The invoice maker checks each one as you type — it flags the missing ABN, watches the $1,000 threshold, calculates GST on the total, and offers the next sequential number.
Invoice problem questions
Why do invoices get rejected in Australia?
Usually a missing ABN, no GST amount shown, no buyer details on invoices of $1,000 or more, a duplicate invoice number, or a description too vague to match to a purchase order.
What happens if I invoice without an ABN?
The business paying you may be required to withhold tax from the payment, so you receive less than the invoice total.
Can I put GST on an invoice if I'm not registered?
No. Only a GST-registered business charges GST and issues a tax invoice. Showing GST you are not registered to collect is a serious error.
Does a small rounding difference really matter?
Yes. Accounting software reconciles to the cent, and an invoice whose lines do not sum to its own total will often be queried or rejected.
How should I number invoices?
Uniquely and sequentially, with a consistent prefix. INV-0042 then INV-0043. Never reuse a number.