1. No payment terms on the invoice
If your invoice doesn't say when payment is due, your client will pay whenever they feel like it. Always include explicit terms: "Payment due within 14 days of invoice date." This also protects you legally — an invoice without terms makes debt collection significantly harder.
2. Missing banking details
A surprisingly common problem. A client wants to pay but can't find your account number — so they set it aside. Later never comes. Put your bank name, account number, branch code, and payment reference format directly on every invoice, every time.
3. Non-compliant tax invoices
If you're VAT-registered and your invoice is missing required fields — your VAT number, the words "Tax Invoice," a separate VAT amount — your client's accountant will flag and reject it. This creates a dispute that delays payment and damages the relationship.
4. Inconsistent invoice numbering
SARS requires sequential invoice numbers. Using dates ("INV-2026-05-14") or random strings makes it impossible to prove sequence. Use a proper format: INV-2026-0001, INV-2026-0002, etc. — and never skip or reuse a number. Invo handles this automatically.
5. No late payment clause
Without a stated late payment policy, you have no contractual basis for charging interest when clients pay late. Add a simple clause: "Invoices not settled within 30 days of the due date will accrue interest at 1.5% per month." Most clients will pay on time just to avoid it.
6. Waiting too long to follow up
The most common invoicing mistake of all: sending the invoice and then waiting silently. Set a reminder to follow up the day after the due date — every time, without exception. One polite message recovers more unpaid invoices than anything else on this list.