给我开个发票。

You usually say this right after you pay the bill. You can add a qǐng (please) at the beginning to be extra polite. Most places will ask for your 'company title' or tax ID. You can show them a picture of these details on your phone. If it is a small shop, they might give you a paper one. In big cities, they will likely give you a QR code to scan. Don't worry, it is a very standard part of daily life.

Use it whenever you need to prove you spent money. This is essential if your company is paying you back for a business lunch. It is also common in taxis if you need a record of the trip. Use it at hotels, big retail stores, and restaurants. Even if you don't need the money back, some people collect them for luck. Some fāpiào even have scratch-off prizes on them! It is like a tiny lottery ticket for being a good taxpayer.

Do not use this at a tiny street food stall. They likely do not have the machine to issue official ones. Avoid using it with friends when splitting a casual bubble tea. It sounds a bit too 'business-like' for a hangout. Also, do not demand it if you are getting a 'special' cash-only discount. Sometimes vendors offer a lower price if you skip the fāpiào. In those cases, asking for one might feel a bit awkward.

The fāpiào system is a huge part of China’s tax regulation. The government uses it to ensure businesses report their actual sales. Because of this, the process is very formalized and digital now. You will often see people scanning QR codes at restaurant counters after eating. It has created a culture where 'getting the receipt' is a standard ritual. It represents transparency and officiality in the modern Chinese economy.

If you want to be more polite, say 请给我开个发票 (Qǐng gěi wǒ kāi ge fāpiào). If you are in a rush, you can just say 要发票 (Yào fāpiào), meaning 'Want invoice.' If they ask what kind, you might hear 电子发票 (diànzǐ fāpiào) for an electronic one. You can reply 对，电子的 (Duì, diànzǐ de) for 'Yes, electronic.' If you need it for a company, say 开公司的 (Kāi gōngsī de).