The status 'not_found' means that users cannot find your app in the search results by the keyword you have chosen because your app is NOT ranked for that keyword. This means that you have to contact support and ask us to terminate the campaign (you will have a refund automatically) and choose a new keyword by which your app can be found in search results among Top 250.
Note: please follow all the instructions carefully while creating the campaign.
On the other hand, if you experience that a little number of installs was delivered but after that, your campaign was stopped with stats as ‘not found’ this means that most of our users cannot find your app by this keyword so the platform is unable to promote it. This happens because Google has personalized the search results which has made it dynamic and hence ranks from search results may vary for different google accounts and devices they use to search for your app. You can try setting the campaign again in a few days, this problem may go away. If NOT then it means we cannot work with this keyword.