Why does Apple's SMS always have a red exclamation point?

Take Apple 1 1 and iOS 14.2 systems as examples. If there is a red exclamation mark on Apple's SMS, it means that the message failed to be sent. Click to enter the information page, hold down the message of sending failure, and click the "More" option. After selecting the message, click the delete icon in the lower left corner to delete it, and the red exclamation point will disappear.

If you find a failed message in your mobile phone, it may be caused by the following reasons:

The SMS center number is set incorrectly. Please re-enter the correct SMS center number in SMS settings.

There is no signal on the mobile phone or the battery is low, which makes it impossible to send short messages. It is recommended to recharge and try again.

The sending format is incorrect. Check whether the sent number is the correct mobile phone number.

Short message cannot be sent due to insufficient balance of mobile phone, and it will be sent again after recharging the phone bill.

The SMS inbox of the other party is full and cannot be received. You need to delete some short messages to receive them.

Being blacklisted by the other party, the message was rejected.

The mobile phone number has no SMS function.

This answer applies to most of Apple's mobile phone models.