You are learning paying the bill: you will read the scene it happens in, learn 10 words and phrases, take apart the pattern behind them (买单 + closing phrases), hear them in a conversation, rehearse them, and finish by saying one thing out loud to be graded.
Any Shanghai restaurant. The meal is over. Asking for the bill in Mandarin is one word — and the payment is almost always done by scanning a QR code. This is the cleanest transaction in the world.
The meal is finished. The lazy Susan is covered with empty plates. The stranger reaches for his phone. His host puts a hand up — he has already paid. The QR code was scanned while the stranger was picking up the last piece of turnip cake.
「已经付了！」 (Already paid!) The stranger protests: 「下次让我来！」 (Next time let me!) His host grins. 「好！说定了！」 (Agreed! It's settled!)
At the door, the waitstaff line up. The host says something and they all laugh — a Chinese proverb about good friends and good food. The stranger nods, not understanding the proverb but understanding the feeling completely.
Outside: 「谢谢今天的款待！太好吃了！」 The host grabs his arm. 「下周再来！」 Next week again. 「好！下次见！」