Bsurfaces tutorial error "specify the name of the object with retopology"

so I’m trying to follow this tutorial:

But, at 28:00 (somewhere around there anyways), when they press add surfaces with the bsurfaces addon, I get an error saying “specify the name of the object with retopology”

I dont know what to do, I selected the thing like they did. The only thing I can think of is it could be because I have multiple curves in different objects, but I cant find a way to merge them into the same object either (since ‘join’ apparently only works with meshes. for… some reason…)