The Prime badge only shows if the customer will receive the item in 2-3 business days.

So you could be looking at your item on Amazon.com from a zip code in Florida, for example, and the Prime badge would show there. And you could change your zip code to California, for example, and it would take 3-4 business days and, therefore, the Prime badge would not show.

Another thing you can do is send more inventory so there are more fulfillment centers in the United States filled with your inventory so more people see the Prime badge.

Also, if your inventory just arrived to Amazon fulfillment centers...you can just wait for it to get received properly so customers can have an estimation of receiving the product in 2-3 business days which would cause the Prime badge to show.