What happens when the iphone sends a text message saying "iMessage needs to be enabled to transmit this message"?

Turn on the short message function and enter the interface of sending short messages like ordinary short messages and imessage short messages.

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In the SMS text input box, we can see that besides the gray word' imessage', there is also a gray microphone icon on the right, which is how to open the voice message!

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Just hold down the microphone icon with your hand and speak into the phone. When you speak, we can see a progress bar with walking time on it, which proves that the voice information has been recorded.

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Then let go of your hand. This is the time stop on the progress bar. After recording, we click on the gray short message symbol (with an upward arrow symbol inside), which is the voice message sending button. At this moment, the voice message came out!

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If you don't want to send it during recording, just slide your finger upward in the direction of the gray SMS icon arrow during recording to cancel the voice message!

Settings-> Information-> IMessage open

Just do it.

If not, log out of Apple ID and log in again for activation.