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An invoice should be issued whenever a transaction requires a payment claim or proof of delivery. Typical situations include:

1. Supplying goods or services between domestic or overseas businesses (B2B).
2. Freelancers or sole‑proprietors billing clients for services or work performed.
3. Export‑import transactions where a commercial invoice is needed for customs clearance.
4. Issuing a pro‑forma invoice before a contract as a quotation.
5. Regular billing for subscriptions, memberships or recurring payments. In each case the invoice serves as a legal record of the amount owed and, for tax purposes, documents the taxable supply.