Thank you for reaching out to our network and for taking the time to share your question. I was happy to look into this deeper for you, and I found that we have an existing tutorial to walk you through resolving this particular error on Facebook.
I believe this is the exact issue you are running into stemming from Facebook Pixel updates for Apple's iOS 14 release. Please read through the linked post for a comprehensive guide for more context and next steps.
Let me know if that helps,
Olivia | Social Care @ Shopify - Was my reply helpful? Click Like to let me know! - Was your question answered? Mark it as an Accepted Solution - To learn more visit the Shopify Help Center or the Shopify Blog