We just released a new Instant Game and we would like to do some user acquisition. According to official Facebook guide we should be able to do it using Install App ad objective campaign. But when we try to set the ad for our app we get the following two errors:

promoted_object[object_store_url] should represent a valid URL (#100)

Please select an app store. (#1885011)

How can we solve this? When we select the app the only App Store setting available is Facebook Canvas and that's the one we set but we keep getting the error. Any help with this will be very appreciated.