Form 1099-K reports transactions processed by your Payment Card Provider. Do not modify the amounts reported on that form.
If you have income in addition to what the 1099-K reports, you will enter it in the same area you used to enter the 1099-K (Other self-employed income. Includes 1099-K, cash, and checks), but adding another row (see sample screenshot)
If the income reported on the 1099-K shows more income than your records reflect, you should contact the Provider to get clarification before your file.
