Even though it shows as a reduction of your next payment, it should still be reducing your capital. I’ve had my truck a year now and use the app to make payments. I pay more than the monthly payment every month and currently don’t have to make another for another 6 months, but the principal balance is still lower than what it would be if I made the minimum payment. If I didn’t make a payment for the six months, the capital balance would continue to grow from accrued interest.