One way to hold this word: you are standing at a till, paying, and money moves the other way — back across the counter to you. The two parts say it , cash and back. What changes between the uses is only whose pocket that money started in: your own bank account, or the seller's.
One branch
錢在買東西的時候往回流
兩個意思共用同一個畫面，只在「錢是誰的」這一點上分開。看句子裡是店員把鈔票數給你，還是賣方承諾事後退錢，就能分辨。
noun · B2
Money that a shop hands you in cash while you are paying with a debit card, adding that amount to the bill so that it comes out of your bank account with the rest of your shopping.
結帳時順便提領現金