I have a red exclamation point next to a text sent me, what does it mean

[AC Question]

When a couple of my contacts text me a message, there is a red exclamation mark next to the text they sent.

 

[the tall guy]

Hi, if the message that you are sending to them has the red ! then it means the message hasn't been sent. I'm not too sure what it means when they send you a message and the red ! is shown - did they maybe send you a picture message and it hasn't been delivered successfully?