AdSense Optimization For Contest Site

I run an online contest platform where most visitors come back daily to vote on entries. Engagement is strong, but my AdSense earnings are not. I want to turn that voting traffic into reliable revenue while staying 100 % compliant with Google’s policies... (Budget: $15 - $25 USD, Jobs: A/B Testing, Ad Planning & Buying, Analytics, Google Ads, Google Adsense, Google Analytics, PHP, WordPress)