From what I’ve read, hiding ads to make money without them being seen is not effective and could even lead to legal issues. What are the criteria for an ad to be considered non-visible? For example, if I have a stack of images that scroll around and I place an ad in the middle and so will not be always visible, could that be a problem? What if another image slightly covers a corner of the ad?
maybe i have a scrollable page how that is considered?
Additionally, what are the consequences if I accidentally use an invalid ad? Is there a way to test ads before production to ensure they are valid?

Just to be clear I currently use flutter for mobile and this is all related to native ads obviusly.

I would like to understand what dynamic designs could be compromising for the ads and so have no legal issues.