Are you talking about the following double entry?
Dr Cash or bank
Cr Interest cap premium
In this case, the credit to the interest cap premium is an income, which is a P&L item. This happens when the interest rate goes above the interest rate cap, i.e. the buyer will get paid the premium. Therefore, it will represent an income for them.
This accounting entry is simplified. Practically, it will happen in two steps. The first includes recording the income and a receivable from the seller. The second will be receiving the cash and eliminating the receivable balance. The simplified entry includes the net of these accounting entries.