Marcus, a cash basis individual, is a general partner in MNOP Partnership. Both Marcus and MNOP use a calendar year for tax purposes. According to the partnership agreement, MNOP pays a $10,000 guaranteed payment to Marcus on the last day of every calendar month. However, because of a bookkeeping error, the partnership did not pay (and Marcus did not receive) his final guaranteed payment for 2018 until January 10, 2019. Identify the tax issue or issues suggested by the situations and state the issue in the form of a question.