Can't add vertex/Vertices to stroke on shape tool.

Good Afternoon.

- Ceated a Rectangle with the Rectangle Tool.

- Disabled Fill. Enabled Stroke width.

- Selected Pen Tool > Add Vertex.

- Pen Tool won't add vertex to stroke.

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- Created Rectangle with Pen Tool.

- Disabled Fill. Enabled Stroke width.

- Selected Pen Tool > Add Vertex.

- Pen Tool adds extra vertex to Stroke.

Does this mean that I can only add vertexes to shapes created with the Pen Tool?

Thank you.