YOU ARE HERE
Messages view - Undelivered Messages
YOU WANT TO...
You want to mark all undelivered messages as "seen".
Step 1: Click on the downward arrow to reveal further sub-categories.
Step 2: Click on Unseen. Your messages will open in the right-hand, black column.
Clear Specific Messages
Clear All Messages
Click on the specific messages you wish to clear.
In the image below, none of the messages are clicked. Notice that the top line says "The user numbers are filtered."
3.1: Click on 1 of the messages you wish to clear.
3.2: Notice that there is a new top line, "Partial Visible" with a downward arrow.
3.3: Click on the downward arrow and choose All Visible from the dropdown menu.
Step 4: Either way (specific messages or all messages), click on More actions (3 dots, gold arrow in image below). Choose Clear Undelivered Label from the dropdown menu (brown box in image below).