Why doesn't my GA revenue match with SM revenue?

The GA revenue figure is entirely dependent on how your dev team setup the GA Enhanced Ecomm tracking. They could be sending gross or net rev, or combo of both. As a general rule of thumb (Google will tell you this too), GA data is by default at least 5-20% off compared to your actual source of truth (Shopify). 90%+ of GA instances out there are in some ways mis-configured. Drop in ReCharge checkout, you are likely missing a lot more data from GA as a result.

Many orders will be missed due to ad blockers and other lack-of-tracking issues. On the UTM source / medium front, we combine what we see from Shopify backend and enrich it with GA data, to create the most comprehensive UTM data possible. The revenue you see in SM is actual revenue, not derived revenue like in GA.