Update - last night (28 Nov) I filled out the form again.
This morning I received an email with the visa attached as pdf. Oddly enough, my "30-day" visa is valid from 29/11/2025 to 28/01/2026
Once again, it notes "Applicant must pay the fee on site / O pedido deve ser pago na fronteira.".
So looks like I'm all set! Will give a final report back post trip.