Companies are not required to send you a 1099-k if the amount is less than $20,000 but they can if they want to. Some companies do it as much for their own bookkeeping records as to help you out. If they choose not to, you simply have to use your own records, though that might be more of a pain for you. The 1099-k and it's requirements are still fairly new and many companies have not adopted them in their own record-keeping systems.
