Why do I have a red triangle with an exclamation point by some messages?

[AC Question]

red triangle with exclamation point by some messages

for three separate people this happens. the message looks like all others and has a date and time. I have checked out one which is to my spouse and it went through. How do I remove the symbol. also does it mean all messages have gone through?

 

[B. Diddy]

Welcome to Android Central! Are they only messages that you've sent, or also ones you've received? The icon usually means there was a problem sending. It may be that your phone initially had problems sending that one message, but ultimately the network got it through. But perhaps some glitch prevented the phone from realizing that.