What should I put on the card sticker to send a text message to China?

You need to add the international code +86. To send a text message from abroad to China, you need to add +86+ the mobile phone number of the recipient. To send a text message from abroad to China, you need to add the international code +86, and long press the 0 key to get a plus sign. The mobile phone that sends short messages needs to support the international short message function.