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So 1 - how do I comment on a question or comment, and 2 - John Brown - does your auditor approve.
Budget an "expense" account for the principal payment like you would interest. Then when you make payments, it's a multi-line entry:
Debit Note Payable principal amount only
Debit Debt Service-Principal "expense" principal amount only
Debit Interest expense for amount of interest
Credit Cash - bank account - full amount of principal and interest
Credit Unrestricted Net Assets Fund (Fund Principal) amount of principal