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Why is there a red number prompt when deleting text messages?

The message has been deleted, and a red number indicates that the network is unstable. The unsent SMS system will resend it, even if the session has been deleted, it will disappear when the system sends it. Short message is a telecommunication service in digital mobile communication system. It is a non-real-time and non-voice data communication service to transmit text or digital short messages through the signaling channel and signaling network of mobile communication system.