You are supposed to report ALL income to the IRS, even if less than the reporting threshold for the 1099 it's reported on. If you ignore a 1099, odds are the IRS will catch it and send you a letter treating it as income -- often without the benefit of exclusions, deductions, etc. that would have been available if you had reported it.
Also, I believe the reporting threshold for the 1099-K was lowered this year to $600 regardless of the number of transactions. The definition of "payment settlement entity" was also broadened to include business payments handled thru PayPal, Venmo, etc.
