I’m trying to sell a sweater. I originally had it marked as “List as Single Item”, but Facebook keeps changing it to “List as In Stock”?

Hi, just as the title says, I’m trying to sell a sweater, but when I posted the listing, it automatically changed it to “List as In Stock,” which is not something I want.

Each time I try to edit the listing back to “List as Single Item,” it just changes back itself. How do I fix this?