Apple Ads functions on an auction basis. Your app should be considered "relevant" to the keyword that matches a particular user query for your bid to make it into the auction. This is called "technical keyword relevance". Apple’s algorithm determines this relevance based on your app category and metadata: title, subtitle, and keywords.
So, if you get no impressions for a keyword regardless of a high bid, it may be that your app’s score is below the relevance threshold. In this case, try to add the keyword to your metadata to improve the relevance and be eligible for the auction.
Here’s how the second price auction works. App 1 and App 2 have higher CPT bids, but Apple Ads ignores them due to low technical relevance. App 4 wins the auction because of a higher bid:
To sum up, when choosing a keyword, consider the following criteria:
Impressions volume. It can be assessed by search popularity.
Competition. It can be assessed by the number of search results.
Technical relevance—the app’s position in search results (preferably <100).
Logical relevance: the bigger TTR and download rate for the app, the better.
Default CTP Bid—the average bid for a category or a given app to reach target KPIs.
According to Neil Patel,
80% of SEOs and marketers do keyword research wrong. They plug in a main keyword to Google’s Keyword Planner, download the results, and then start sorting through them in a spreadsheet. But here’s the thing: literally thousands of other marketers have already searched the exact same keyword.
Hence, it’s vital to discover uncommon keywords which are still likely to bring value.