I am displaying dfp ad inside my mobile android app
The id of the dfp ad looks like this:
/1234567/game_intertitial
/1234567/game_intertitial?cust_params=bid=5
So the answer is to use to use the sdk for this like this:
final PublisherAdRequest adRequest = new PublisherAdRequest.Builder()
.addCustomTargeting(key, val)
.build();