Give the flat-lay some structure
A shaping brief photographed flat on a bed is a crumpled beige shape. Nothing in it says firm control panel, silicone grip at the leg or a high waist that doesn’t roll down. The flat-lay has to show the engineering, because that is what the buyer is paying for.
Before you upload, smooth the garment on a firm surface in a contrasting colour and fold it so the waistband and one leg opening face the camera. If there is a panel seam, a gusset or a hook-and-eye closure, let the light fall across it rather than flattening it. The generator works from what your photo shows, and a seam it can’t see won’t appear in the result.
For bodysuits and slips, a hanging shot often beats a flat-lay. Hang the garment on a plain hanger against a wall so the shape and the length read, then use that photo as the source for the white-background image.