If it is literal gambling, they can’t. I know one state that runs a lottery, and has an app, but it has to be side-loaded from lottery’s own website.
Paying people for taking surveys or watching ads is not gambling. it is employment and hence legal. There might be taxes involved, but only when (and if) you actually pay them.
Also, plenty of apps are lying, both in their ads and when registering at the app store.
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