Apple's mobile phone sends a message to the other party to display the clock diagonal line.

The diagonal line of the clock indicates silence, which should appear after long pressing the volume reduction key. As for the short message, if it turns blue, it means that it was sent successfully. If the message has an exclamation point, it means that the short message was not sent successfully and failed to be sent. Open the message, click the red exclamation mark, and then try sending it again. If the red exclamation mark is still displayed after the first step, open the phone settings and click on the information page to find iMessage.

Open the message again, repeat step 1, and then resend the message. At this point, the transmission was successful.