Problems with attribute names

Hi Guys!

I’m trying to import variable products. In fields, where I got only one word attribute name, it’s working (Armrest), but when I try to add attributes to the group “Chair base” it wouldn’t understand it. I tried the name “Chair base” and the slug as well “chair-base”. Shall I go more deep? Or the slug is not correct, it should be something like “pa_chair-base”?

Thanks