The dimension under the cursor simply won't be placed after I click on the desired land site

Attempted steps:
Smart dimension tool > Click on the edge I want to measure > Drag the dimension to where I want it

A gray dimension is offered instead of blue. I suppose it means a driven one. Exactly what I need.

I can select the edge, but not place the dimension

If I try to pick a vertex on one end, it won't let me pick the vertex on the other end

Why is this happening ?

EDIT:
Important information: It's under a sketch. I'm using sketch smart dimension, not free smart dimension