Why didn't you make an anthropomorphic expression?

Cannot send because the other party is not using iMessage.

Ask the other party to reset. After the setting is completed, close the running SMS sending program or restart the phone. The so-called disconnect you at the same time. DID you enter the id?

First, open the settings indicated by the arrow on the mobile phone desktop. After opening the settings, click the shutdown flight mode to ensure the smooth network.