Let the seller keep making the payment. It turned into a 45 day late.

Short version for anyone about to do their first one. Sub-to means the loan stays in the seller's name and I take over the payments. On my first one I set it up the lazy way: I sent the seller $1,275 on the 1st by bank transfer, and she paid the mortgage from her own account, because the autopay was already set up and she said it was easier.

Month four she had a car repair. My $1,275 went to the shop. She didn't tell me. I found out when the servicer's late notice went to her old address, which was now my rental, and my tenant texted me a photo of it.

By then it was 45 days past due. It cost $86 in late fees, a 30 day late on her credit which is the one thing she asked me to protect, and a very bad phone call. The loan didn't get called. It could have. A late payment is the fastest way to get a servicer looking at a file, and looking at the file is how the due-on-sale clause stops being theoretical.

Fixed it by putting the loan on a third-party loan servicer. I pay them, they pay the lender, and I get a statement showing it happened. Costs me $32 a month and I would pay five times that.

What I'd do differently: never route a payment through the seller. Not once, not as a favor, not because autopay is already set up.