When I asked about Google adsense or ads for games, the answer was something along the lines; Google restrictions, you need at least 500, 000 plays per month and some other things.
Well, then how about CPM Star? This would cover mobile and web in one swoop.
Those from the Flash era ( 2005 - 2015 let's say ) should know what I am talking about.
I personally had about 2 years where I made around $100 per day from CPM Star. That is Construct 3 subscription money each day.
It shouldn't be hard to do. Pre-loader ad, and between levels or end game ads.