The IRS Form 1099-K is a tax report that broker-dealers (and some cryptocurrency exchanges such as Coinbase, Gemini, Robinhood, etc.) generate. They keep one copy for themselves, send one copy to you (the user), and one copy to the IRS. This form essentially shows aggregate transaction volume per month.

IRS guidance note has clarified that cryptocurrency is taxed as property, meaning that the capital gains tax is calculated based on the difference between the fair market value at the time a crypto asset is disposed of and the cost basis at which the asset was acquired. The 1099-K includes none of this information. Instead it simply sums the total proceeds of cryptocurrency dispositions across all transactions. This cannot be used to correctly file cryptocurrency taxes.

Therefore the IRS clarifies that you need to use Form 8949 (which is what is generated by CoinTracker) to file your cryptocurrency taxes (source: IRS, A40). The 1099-K helps the IRS understands who are high transaction users, however those numbers are not actually used in your tax filing.