Primitive/line doesn't display anything after setting points

I’m following the following tutor

if I do set the points A, B with the cursor, and manually (by inputting the cordinates), nothing is displayed, why?

It looks like it’s always taking the same point and you have A point and B point the same which will result in a line with no length, you can make sure if it’s true by taking “Length” component and plug it in to L output. If the result is 0 then you have a line with the same start point and end point.

Try to click different points in the perspective. It looks like it’s always taking some odd point in the middle.

Your solver is locked. Unlock it.

Second thing: you have to unlock the solver. Right now you have this lock displayed = solver is locked, nothing will be calculated. To unlock solver click middle mouse button and click to unlock it.