Meta Ads Campaign Optimization for In-App Purchases

I'm seeking an experienced digital marketer specialized in Meta Ads to improve the performance of my ad campaigns. The primary goal is to increase in-app purchases, which have been declining over the past few months despite consistent targeting of a specific demographic (age group and geographical location).

Key requirements:
- Analyze and refine the current ad strategy
- Improve CTR and Cost per Result metrics
- Leverage Facebook's Advantage+ feature effectively
- Propose and implement cost-efficient solutions

Please provide evidence of your past successes with similar projects.