Having problems with boundary filling a sclupt

[takacosu]

Greetings,
I have a sculpt and trying to make it a solid body. I projected to the bottom plane and extruded it but when I select the extrude, sculpt and bottom plane, nothing turns green.
I have done this before without a problem but Im not sure when it wont work this time.

I included my project here
https://a360.co/2RB4dcV

Thank you 

[mavigogun]

That link is not publicly accessible.    Just File>Export>save local>and Attach the F3D document in reply to this thread on the Forum.