If you can't see the Facebook Like button on your Coupon Pop, it's most likely because your fan page has restrictions which prevent the Like button from being shown to certain users.
This can happen if you restricted the display of your page to certain geographical locations or age groups.To confirm if this setting is in place, go to your account permissions as displayed in the following images.
It's very important to make sure your business page is open in order to be able to sell your products to all relevant customers. For example, if you set a rule like "Age Restrictions", and your potential customer is NOT LOGGED into Facebook, then their system cannot read the user's account to detect if any of your restrictions are met. Since Facebook can't read anything, they will not see the "Like" button. Make sure your settings do not include any restrictions (like country restrictions for example).