The app embed injects Notify Me on your storefront. Widgets do not appear until the embed is On for the theme customers see.
Open the embed from Notify Me
On the home dashboard, find the app embed card. Choose Enable if the badge is Off, or Manage if it is On.
Turn on Notify Me — Back in stock
The theme editor opens App embeds. Enable Notify Me — Back in stock, then save the theme.
Refresh status
Return to Notify Me and choose Refresh status. The card should show On.
Enable the embed on your published theme. Turning it on in a draft or unpublished theme does not show the trigger to shoppers.
If the card says Unavailable, open the theme editor from the card and confirm the embed is listed for that theme. Then see The Notify me button is missing.