How to get rid of the orange triangle sign on one of my text message?

In my messaging, there is an orange triangle sign in one of my sender and it keeps listing on the first regardless of how many sender of sms I sent. Any idea how to get rid of this orange thingy? I believe it got something to do with 'Favourite' sms.

The triangle usually means a message in that thread failed. Please open the thread with the triangle sign and check if there are unsent message.

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