Cannot subtract because object isn't a solid

Hi, I am trying to make this shape for a building I am designing, It consists of this one long curve piece that needs to be flush with the side of the building, I plan to do this my using the subtract tool on that curved piece with a triangle that has the same profile as the building. However when I try this, the curved piece is not a solid, even though I made it into a component and created the shape through follow me tool?
Concep1 experimentation.skp (3.9 MB)

Help please!

None of these guarantees that the model is solid.

Then how would I achieve the result I am looking for?

By attaching your model rather than a screenshot so we can tell you what is wrong with it.

updated to include my file!

There are two stray edges. If you switch to the Xray style and zoom in you’ll be able to see them.

I don’t know if SketchUp for Schools includes Solid Inspector. SketchUp Go does. It would help you find these little tiny edges that are preventing the object from being solid. Otherwise you just have to dig. Again, using the Xray style makes it easier to see inside the objects as you look for problems.

Thank you so much! I used to xray and solid inspector to find the stray edges and make it as a solid, and the subtraction worked!