AI agents for business finance: what they can and can't do
What AI agents can do in bookkeeping, close, collections and compliance today, where a person must stay in charge, and how to judge a product.
The short answer
Give every invoice a unique number in one unbroken sequence, for example INV-2026-0001, INV-2026-0002, and never reuse or skip a number. The Nigeria Tax Act 2025 lists the invoice number among the details a VAT invoice must show, and under NRS e-invoicing each invoice also gets an Invoice Reference Number. Gaps and duplicates make a tax officer ask what is missing.
Invoice numbers look like admin, but they are how you, your customers and the tax authority tell invoices apart. A clean sequence lets you prove you have declared every sale. A messy one invites questions you would rather not answer.
What the rules say
Under section 153 of the Nigeria Tax Act 2025, as summarised by Mondaq in May 2026, a VAT invoice must contain:
- the supplier's Tax Identification Number
- the company incorporation or registration number
- the invoice number
- the supplier's name and address
- the date of supply
- the purchaser's or client's name
- the gross amount of the transaction
- the VAT charged and the rate
The law asks for an invoice number; good practice is to make it unique and sequential so it works as a control.
E-invoicing
The Nigeria Revenue Service is rolling out e-invoicing through the Merchant Buyer Solution (MBS). According to The Guardian in July 2026, large taxpayers (turnover of ₦5 billion or more) had to comply by 31 July 2026, medium taxpayers (₦1 billion to ₦5 billion) began onboarding in July 2026 with enforcement expected in early 2027, and smaller taxpayers follow, with full adoption targeted for January 2028. Each e-invoice carries an Invoice Reference Number (IRN), and buyers are told to accept only compliant e-invoices. Your own number still matters: it is how your records match the IRN. See e-invoicing in Nigeria.
A numbering scheme that works
| Format | Example | Good for |
|---|---|---|
| Plain sequence | 0001, 0002, 0003 | Very small businesses with one invoice book |
| Prefix + year + sequence | INV-2026-0001 | Most businesses; restarts or continues each year |
| Branch code + sequence | LAG-INV-0457, ABJ-INV-0112 | Multiple branches, each with its own series |
| Separate series for credit notes | CN-2026-0001 | Corrections that reference the original invoice |
Four or five digits after the prefix are usually enough for a year. If you issue thousands of invoices a month, use six so the numbers sort correctly in a spreadsheet.
Pick one format and stick to it. If you restart the sequence each year, the year in the number keeps every invoice unique.
Why gaps and duplicates cause problems
- Gaps (0041 then 0043) suggest a missing invoice, which can look like an unrecorded sale. Keep cancelled invoices, mark them "void", and keep the number used.
- Duplicates (two invoices numbered 0050) confuse customers, delay payment and make your sales total unreliable.
- Edited invoices after sending break the record. Correct with a credit note instead; see resolving an invoice dispute.
- Mismatches with e-invoicing: if your system and the IRN record do not line up, VAT input claims by your customer can be questioned. The Guardian reports that non-compliance can lead to fines, interest and restrictions on VAT input credits.
Worked example
Example: a caterer issues INV-2026-0118 for ₦250,000, then the client cancels. Instead of deleting it, the caterer marks it void, keeps the copy, and issues INV-2026-0119 for the next job. Later, a client disputes ₦40,000 on INV-2026-0121 for ₦600,000; the caterer issues CN-2026-0007 for ₦40,000 referencing 0121. The net sale is ₦560,000 (₦600,000 minus ₦40,000) and the sequence has no gaps.
Common numbering mistakes
- Numbering by customer. "ACME-1, ACME-2" style numbers repeat across customers and break the single sequence. Keep customer codes in a separate field.
- Using dates as numbers. "19102026" fails the moment you issue two invoices on one day.
- Restarting when you change software. Carry the last number into the new system and continue from there.
- Pro forma invoices in the main series. A pro forma is a quote, not a demand for payment. Give it its own series (PF-2026-0001) so cancelled quotes do not leave gaps in your invoices. See pro forma vs invoice.
- Hand-written books with missing pages. If you still use a receipt or invoice booklet, keep every carbon copy, including spoilt ones.
What a tax officer looks for
During a review, an officer can compare your invoice sequence with your bank credits and your VAT returns. An unbroken sequence that reconciles to the bank makes that comparison short. Each unexplained gap becomes a question, and voided invoices you kept answer it quickly. The same discipline helps your own management: a monthly count of invoices issued is a simple sales check.
Steps to set it up
- Choose a format and write it down.
- Use one system (software or one invoice book) per series.
- Never let two people issue numbers from the same series by hand at the same time.
- Keep every invoice, including voided ones.
- Each month, list the numbers issued and check for gaps.
Where Pryme fits
Pryme invoicing numbers invoices in sequence, and the Finance agent can prepare a monthly list of invoices and credit notes for you to review.
Questions people ask
What is the correct way to number invoices?
Use one unique, unbroken sequence, for example INV-2026-0001 onward, with a separate series for credit notes. Never reuse or skip numbers.
Does Nigerian law require an invoice number?
Yes, for VAT invoices. Section 153 of the Nigeria Tax Act 2025 lists the invoice number among the required details.
What is an IRN on an invoice?
An Invoice Reference Number issued under the NRS e-invoicing system (Merchant Buyer Solution). Large taxpayers have had to use it since 31 July 2026.
Can I delete an invoice I sent by mistake?
Do not delete it. Mark it void and keep it, or issue a credit note, so your numbering has no gaps.
Sources
- Mondaq: Examination of the VAT provisions under the Nigeria Tax Act 2025 (28 May 2026) · accessed Oct 2026
- The Guardian Nigeria: NRS sets July 31 e-invoicing deadline (27 Jul 2026) · accessed Oct 2026
This article is general information, not financial, legal or tax advice. Products described are provided under the terms on this site and are subject to regulation and eligibility.