Redirect, do not pause
Exclude the unavailable items, move the budget to what you can ship, and keep the campaign structure and its history intact.
Sync availability fast
A feed advertising sold-out items wastes spend and risks a mismatch finding. Daily is often not fast enough during a sell-out.
Protect the winner’s history
If your best seller is out, resist restructuring its campaign. You want it back exactly as it was when stock returns.