I was thinking about how you could add your own ad system to a game, someone could pay a certain amount and they could request for there game to be added as an advert, and like in mobile games, people can see an advert (probably an image with details) and get an in-game boost.
But is this against the TOS?
So far as I’m aware, this isn’t against the ToS - There’s many games that offer this form of advertisement. Pay2Display banners etc.
Recruitment Plaza especially does this, you can pay R$ to display your ad in game.
As far as I know it isn’t; there has been a platform-wise ad system (ro-ads or something). But why should you? It is hurting your game quality.
It’s not against ToS, take trade hangout for example, you can advertise your game/group.
Yes, this is allowed. 
Countless games exist that rent out space to other groups, such as the Group Recruiting Plaza or even restaurant games that have adjacent clothing stores.
@boele009 Hardly. A lot of games that do rent out space aren’t lacking in quality at all.
I don’t think its against ToS, as long as the contents for the ads itself is following the rule. And think that is what you need to maintain or taking care. Not sure if this is a good monetize system tho as @Boele009 mentioned.
He isn’t talking about renting out space like clothing stores, but more as annoying pop-up ads on mobile (if I read his post well).
@Boele009
They don’t have to be annoying. You can have them voluntarily watch ads for sweet rewards. Plus, it gives them a break if they don’t like ads instead of sitting in front a screen all the time. Sure, certain apps in the app store can be annoying with excessive ads, but the quality apps have them off to the side or give a choice to watch them.
@OP
I’m just worried about the management of it. How are both sides going to agree on how many people have seen a certain ad? Maybe I’m overthinking this, but the people running the ads need to verify that their ad is being shown successfully. For example, what if the image fails to load. And now with video frames, how do we make sure that it doesn’t break? Also, how do we make sure any exploiter can’t remove the banner/video from their screen all together? There are many factors in this, but if you can pull it out somehow, this is going to do a lot of good you and your game.
Just make sure you don’t make it annoying, make it voluntary.
Same goes for Windows XP Simulator (i think), they have ads for like 9 Robux
Like in a game if you wanted a boost you could click a button in the shop menu, and you could have an add for another game pop up, and then after about 5 seconds later it would close and grant the reward, it isn’t going to be a really annoying thing where they pop up constantly
I believe the conclusion we came to in this thread was that they’re ok. so long as you work in robux exclusively.
Please thoroughly search the forum before posting, it helps reduce duplicate threads 
In-game adverts are not against ROBLOX’s Terms of Service. Infact, many games use this system such as Group Recruitment Plaza.
Hope this reply can help you. Have a nice day, and good luck with your game!