Is this abusing Unity Ads?

So I have made (and completed) an app that includes advertising using Unity Ads. Within this app, I have a menu you can go to to support the developer. Since I don't have a website to use for donations and of the such, I decided to make it so that they could watch an advertisement (nonskippable one) to support the developer. The thing is, at the moment, there is no reward, so it is just a button for an advertisement. There is a 60 second cool down however. Right now there is no reward, which might change in the future if I can come up with something worth the user's time. I was just wandering if this was ok or if it was noted as a way the user could spam ads for me. I think the 1 minute cool down is enough to make it legal, but I'm willing to make the cool down longer. Thank you.