I can not select a line/spline in revolve

#1

After drawing a circle,I then draw a line through the center of the circle.I select revolve and select the semicircle as the shape. select ‘next’. I am unable to select the and get the message about it being the wrong type of line. I also have a similar problem with union etc

#2

Hello, welcome to the Shapr3d community.
Drawing the Revolve guideline through the semi-circle or closed arc will result in having two closed sketches and hence an invalid geometry for revolving. Instead, draw the line parallel to the closed sketch. Here’s the link to our short article on the Revolve tool:

I hope this is helpful.