Apple watch sends text messages instead of iMessage.

If you don't use iMessage when sending text messages on Apple Watch, it may be because you don't have iMessage enabled on the iPhone or your carrier doesn't support iMessage. To solve this problem, you can try the following steps:

1. Open the Settings application on iPhone, and then go to Messages or SMS options.

2. Make sure iMessage is turned on. If it is not open, please click the "Open" button and enter your Apple ID and password.

3. If your operator supports iMessage, please confirm that your mobile phone is connected to Wi-Fi or cellular network.

If the above steps still don't solve the problem, you can try to restart your iPhone and Apple Watch, and make sure that your Apple Watch is connected to iPhone, cellular network or Wi-Fi. In addition, you can also try to send an iMessage on Apple Watch to see if it can be sent successfully.