What should I do if texting between iphone turns green?

Text messages between iphone turn green. It may be that the other party doesn't have a number, doesn't activate iMessage, doesn't connect to the Internet or doesn't use Apple devices.

When the iphone SMS sending key is green, the representative sends ordinary SMS, and the operator charges the corresponding fee;

The SMS Send button is blue, indicating that iMessage can be sent. IMessage is an instant messaging software launched by Apple, which is only available to users of Apple devices (you need to log in to apple ID and open iMessage). Users only need to support data through WiFi or cellular network, and Apple devices will automatically identify whether the mobile phone number is an iMessage-enabled user. When both parties are iMessage users, communication can be completed.