Facebook and Google are both blocked by Apple on occasion, so they are roughly 80% accurate. For the most accurate data, we are working on pulling data directly from Shopify and other platforms.
Google data is in real-time, and it measures up to 100% of the cash conversions happening that day. On the other hand, Facebook ad account data is faster and broader, but less reliable, as it only measures purchases happening from ads. Facebook pixel data is more reliable than the Facebook ad account, as it measures the entire website (including the sales funnel).
All platforms that track conversions are currently blocked on some iOS devices and Safari browsers.