To use the Amazon coupons on their website, you need to meet the conditions:

•  The items you choose must meet all coupon requirements as explained in the Terms and Conditions.

• The coupon has not expired. 

• The seller uses the Amazon checkout system or a customized checkout system that accepts the coupon.

To avoid this problem, you should check out carefully Amazon promo code before that promo code could be expired, some promo codes are tied to a minimum purchase, a first-time purchase, or tied to geography, and other reasons.

Usually, Coupon Stacking is not allowed at Amazon. However, the store will surely give out notice if available.

There is no certain number for the frequency of releasing coupons from Amazon. But, most of the time, there will be at least one available. Special Discount Days such as Black Friday, Cyber Monday, Back to School Sale... come with many coupons.

Yes. Coupons for each Discount Event of Amazon will be collected here while being updated day by day. Sometimes, there will be deals not updated promptly but it's rare, we expect sympathy from you. 

All deals from Promotion Programs of Amazon are collected here. For each certain occasion, its coupons will be on the top of the coupon list, and surely they always come with an expiry date.