Name the impact without exaggerating it
Describe who had to wait, worry, redo work, spend money, or make a choice with incomplete information. For a message about how to apologize for a message sent to the wrong group, use this factual base: name the post, message, file, audience, and privacy impact as precisely as possible.
Make repair practical
Offer the repair you can actually complete, with ownership, timing, and any limit stated honestly. Delete or correct what you control, notify affected people, and preserve evidence needed for a formal response. Make the immediate next step clear enough that the recipient can answer without reconstructing the entire history.
Let future behavior carry the proof
Do not repost the harmful material inside the apology or blame the platform for your choice. Escalate intimate images, impersonation, account compromise, threats, and personal data exposure through platform and legal safety channels. A promise inside a message is weaker than a visible change in what you do after it.