How can you eat chometz after shvi’i shel pesach which “was sold to the non-Jew according to Halacha” It still belongs to the non-jew.
What if he tells you, “It’s OK, go ahead and eat?”
(And don’t tell me that you can’t because you can’t make a kinyan on Shabbos. You don’t need to make a kinyan to eat someone else’s food with their permission. When you’re a guest at a Shabbos table and they make hamotzi, I’m sure you don’t make a formal kinyan on your challah before you eat it.)