This would be considered 2018 income.
Under the cash method, you include in your gross income all items of income you actually or constructively receive during the tax year. If you receive property and services, you must include their fair market value (FMV) in income.
Constructive receipt. Income is constructively received
when an amount is credited to your account or made
available to you without restriction. You do not need to
have possession of it. If you authorize someone to be your
agent and receive income for you, you are considered to
have received it when your agent receives it. Income is
not constructively received if your control of its receipt is
subject to substantial restrictions or limitations.
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