Optimize Meta Ads to Shopify

I’m currently running Meta campaigns that register about 100 link clicks, yet the tracking shows barely 50 landing-page sessions and only four visitors reaching my Shopify store. I need to understand— and fix— why the numbers fall off at both stages of the funnel... (Budget: €8 - €30 EUR, Jobs: A/B Testing, Analytics, Conversion Rate Optimization, Digital Marketing, Google Analytics, JavaScript, PHP, Shopify)