This has come to my attention reconciling my Koinly 8949 with the Coinbase 1099-DA being sent out. If you import Coinbase via API you get mismatches in proceeds if you use Coinbase advanced to trade and receive fee rebates. An example:

You own 1 $btc. You sell the $btc on Coinbase Advanced for $100,000, the platform has a fee of $500 but then rebates you (via Coinbase Pro) for $100. So in total you receive $99,500 + $100 = $99,600.

Coinbase, on their 1099-DA (and on their csv reports etc.), is counting the full $99,600 as PROCEEDS. Koinly, on the other hand, only counts $99,500 as proceeds, and then adds $100 as a separate "Fee refund" transaction. This $100 does NOT get counted anywhere as proceeds, meaning if this was your only transaction for the year, the 1099 will report $99,600 of proceeds and the 8949 only $99,500. This is a small but meaningful mistake now that the IRS is looking for mismatches such as this.

(A similar mistake is happening on the buy end, i.e. Coinbase subtracts the fee rebate from cost basis and Koinly does not, but this is less pressing as it doesn't mess with the 1099-DA proceeds.)

This is somewhat urgent and needs to be fixed before Coinbase Advanced x Koinly users can file their taxes properly.