Your friend request was not accepted by the person.
A message that is marked as pending usually means that the person you are trying to reach has not accepted your friend request. The discussion box will display the warning, “Your Snaps and Chats are pending until user> adds you as a buddy.” You might remind them to accept the request on their end to fix this. read more what does pending mean on snapchat
They unfriend you on Snapchat how to know
They probably unfriended you if your messages used to be delivered and you suddenly started getting the pending status. To find out if someone has unfriended you, look up their name in the friends list (Bitmoji or profile symbol -> My Friends). You will need to wait till the person adds you back if that is the case. If it’s urgent, you can try messaging them somewhere else till then.
You were blocked on Snapchat.
Someone may have blocked you, which is another reason they could not be reading your message. Keep in mind, though, that when someone blocks you, the messages will appear as “Delivered” rather than “Pending.”
Deactivating or cancelling a user’s Snapchat account may result in a pending message status. There isn’t much you can do to communicate them in this case unless they wish to restart the account.
The message was misplaced.
Snapchat automatically deletes all unseen Snaps after 30 days. If a Snap you send to a friend hasn’t been opened in a month, it will appear as “Pending” on Snapchat. If the communication is critical, you might choose to resend it now.