How do you track which periods the amount received covers?

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Here is the situation we are having a challenging time managing: A standard PO is created for a service and the supplier is expected to bill monthly for 3 periods. The requester chooses to receive the full PO amount up front the first month, which creates an accrual entry for the entire amount the first period. We do not have a way in Oracle to determine how much of the PO amount should have accrued the first period, the second period, etc. Is there a different type of PO we can use that allows us to track this?