How do I say 'receipt / invoice'?

The English word “receipt” maps to three different Chinese words, and using the wrong one can confuse both you and the vendor:

• 小票 — the store printout. This is what a cash register spits out. It proves you paid. You get it automatically at supermarkets and chain stores. This is what you want 90% of the time.
• 发票 (fāpiào) — the official government tax invoice. This is a legal document with the business’s tax stamp. It matters for company reimbursement, tax deductions, and official accounting. Businesses are legally required to issue 发票, but small vendors may resist because it triggers tax liability.
• 收据 — a formal receipt, often handwritten and stamped. Middle ground between 小票 and 发票.

When you just want proof of purchase: 小票. When your company is paying and you need to expense it: 发票. When you need a formal acknowledgment that money changed hands: 收据.

Pro tip: saying 开一下发票 at a restaurant often prompts “没发票” from small places. Larger restaurants and hotels will print one without issue.