Once I accompanied a domestic delegation to visit the United States. After dinner, we asked the waiter for an invoice, but the waiter did not know what an invoice was, so we talked to the boss and explained to him that we need an invoice so that we can be reimbursed back in China. The restaurant boss listened to us with great bewilderment. He asked, “Aren't you eating for yourselves, so why are you having the government pay for it?”
When travelling on business, asking for a receipt to be reimbursed is very normal. Perhaps the problem was asking for an "invoice" instead of a "receipt"?