Mess up with a friend? Fix it with them directly. Sending a mutual to smooth it over just adds a middleman.

Repair does not transfer. When you send somebody else to do the talking, the message your friend receives is that you could not be bothered to face them, and the go-between now owns a version of the story that is not yours. Every retelling drifts a little. By the time it lands, the apology has turned into a report about an apology.

Go to them yourself, in person if you can manage it, and keep it short. Say what you did and what you got wrong, and do not bring a witness. If they are not ready to talk, leave the door open and wait rather than recruiting help.