If you can make an overpayment, namely picking Regular Payment and then insert an amount, that will work regardless of lender for what we're talking bout.
If you can't do that, like if it's due amount or bust, I'd try Other Payment and see what it did: the fact there's another option besides princpal only suggests that it is an off-cycle regular payment.
I'm fairly certain I can just hit Regular Payment and then put more than the monthly. I do that with my car payment and it always works. I get a little warning saying that I'm paying more than required and it may affect my due date, so I'm assuming the same thing will happen here. I get paid on the 10th, so I'll make my payment then and check back and let you know how it went!
I’m probably never finding that garden everyone keeps talking about.
Officially collection free as of 3/19/19!! STARTING SCORES: 377(11/2013) & 580(3/2018)