Chase doesn't determine the merchant codes. Instead, "Merchants who accept Visa/MasterCard credit cards are assigned a merchant code which is determined by the merchant or its processor... based on the kinds of products and services they primarily sell." Chase then groups similar merchant codes into categories for determining eligibility. Sometimes the merchants don't provide a merchant code that falls under a category created by Chase. This is why you may sometimes make a purchase on something that you think should activate the travel credit but it fails to do so. If you think a purchase should have activated the travel category but it didn't you can send a secured message to Chase to request them to review it. However, your success will vary and Chase might just refer you to their terms which do not obligate them to honor your request since they aren't responsible for assigning the merchant codes.