Ad tracking of e-commerce

I'm posting ads on Facebook and Instagram and I want to be able to track the purchase conversions of these ads in Google Analytics.

When using Big Cartel I can not track conversions using the UTM parameters because the payment process linked to Pay Pal and its automatic redirect is not reliable

Is there any way to use the UTM parameters or another technique that can show me accurate data about the purchases that are obtained from clicks on my ads?

I have researched in Shopify but I have noticed the same problem.

Because the verification process leaves my domain and returns to make the payment, you can not work with the targets of the destination URL.

I read this and I was wondering if this is a way to solve the problem.

"Google Analytics tracks visits to your paid pages by using a function to change the name of the page view on each of your paid pages." Google Analytics uses this page view as the URL, so it can use relative links in your Objectives and funnels definitions despite is different from the domain of your store. "

Is there any way to actually get ad purchase data on e-commerce platforms or an e-commerce platform that does not link the payment process?

Thank you