As a landlord, financing costs should not be expensed. Instead, you can record these costs on the Tax tab, under the Property Earnings income source details. Answer yes to I have financing costs, such as mortgage interest, to expense.
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Be sure to include interest and other financing costs, but not the repayments of your outstanding mortgage or loan.

Please note, if you're reporting self-employed income and looking to include financing costs on your tax return the rules are different, take a look here.