Amazon Deals API category_id: Why It Silently Returns Fewer Deals
The category_id parameter on /amazon-deals is never validated: an unknown department slug is not rejected, it is passed straight to Amazon's filter and just returns fewer or no deals, billed like any other answer. Check category_id against the real category tree before you call, the same way /amazon-bestsellers is checked, because here there is no error to catch a typo after the fact.