Bezier Cad merge ends (can't figure out)

Noob question!

Trying to merge curve ends with the Curve Cad plugin. I can’t to find the steps anywhere online just that the function is there. Tried all the following then executed the merge ends command.

Tried selecting start end points in edit. Tried Joining curves first then selecting start /end points, Tried selecting all points.

Keep getting “invalid selection.” I’m sure its very simple.

Delete one of the endpoints then use ALT+C to toggle cyclic.