Write with AI drafts a reply in the Unibox composer and needs at least one message on the thread. It never sends, so you still select Send.
Give it a message to draft from
An empty thread cannot draft. The button stays off and the hint is "Need a message to draft from."
Open the Unibox thread that already has a message.
Select Write with AI.
Wait for the composer to fill.
Edit the draft if you want, then select Send.
If you already edited the box, clear it or accept that Write with AI will not replace your text. The hint is "Edit or clear to draft again."
A failed draft shows "Could not draft. Try again." Stay on that thread and select Write with AI again. Do not open a second thread to force a draft.
If it still does nothing
Confirm the thread is not empty. Confirm you did not type over the last draft. Write with AI only fills the box. Account Protection still runs on Send. If Send is blocked, that is a different article.