Placing Structural Foundation: Walls

Hi,
I’m trying to place structural foundation walls by selecting the specific walls e.g. Basic Walls - 215 Blk. I’m struggling to make this work. I can place isolated foundations but not strips directly under walls. I’ve search the forum and can’t seem to find a solution. Apologies if this is a fairly basic topic.

Thanks.

Pudiste encontrar alguna solución ?