We always recommend using our Inventory Protection feature to make sure your listing is protected, but if for some reason you are unable to use or set this option, you can consider setting a max quantity from your Seller Central account directly.
Please go to your listing in Seller Central and click in the 'Offer' tab, there make sure the Advanced View button is ticked ON, it will turn orange as seen below:
Scroll down to the 'Max Order Quantity' box and there, you can set a limit on the number of products that a Buyer can purchase per order they place:
We recommend keeping that to 1 or 2 while the Promotion is active, then click the 'Save and finish' button.
Remember, this will be the number of units a buyer will be able to buy per order and it will also affect how many your regular Amazon buyers can purchase since the limit set here will apply to the whole listing. If you set the Max Order Quantity as 1 that means that buyers will only be able to buy 1 unit in that transaction. If they want to buy more than that, they can always place another order.
The max quantity can be changed or removed at any time and we recommend taking it off after the promotion is over.