Tracking e-commerce ads

I advertise on Facebook and Instagram and I want to be able to track the conversions of buying these ads on Google Analytics.

With the help of Big Cartel, I am not able to track conversions using UTM settings because the payment process related to PayPal and their automatic redirection is not reliable .

Is there a way to use UTM settings or another technique to get accurate data on purchases from clicks on my ads?

I have reviewed Shopify but I have noticed the same problem

Since the payment process is leaving my domain and returning to checkout.shopify, the destination URL goals do not work.

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

"Google Analytics tracks visits to your payment pages by using a function to rename the page display on each of your payment pages." Google Analytics uses this page view as a URL. / being different from the domain of your shop. "

Is there a way to obtain purchase data from advertisements on ecommerce platforms or an ecommerce platform that does not link the process of payment?

thank you so much