What do you mean the message has been sent but rejected by the other party?

Wechat sent a message to the other party, and the other party refused, because the other party had blacked you out, and the message you sent was unacceptable to the other party.

You can try to contact each other in other ways and ask them to cancel your blacklist. Cancel the blacklist on WeChat-Me-Settings-Privacy-Address Book blacklist. If the other party cancels the blacklist, you can send him a message again.

Or you can click on his avatar in the window with his partner and click on the top right corner ... to delete the partner.

If you are friends in real life, it is not recommended to delete each other directly. Let's call each other and see if it's caused by his misoperation.

Under normal circumstances, it will not be hacked, or it may be because something bad has happened between friends, and we need to resolve the misunderstanding and solve it slowly.