I booked a round-trip ticket from Chongqing to Changsha online. Why did the SMS only receive the departure notice after the bank card payment was successful, and there was no return trip?

Domestic round-trip air tickets are actually two air tickets. You should have two e-ticket numbers. Did you receive two e-ticket numbers in your short message? If so, it is right to remind you to change your boarding pass on the way. After you get on the plane on the way, you may send a text message to remind you to change your boarding pass on the way back so as not to confuse you. I suggest you find the customer service phone number of China Eastern Airlines for confirmation.