In order for the addon to work you need to merge at least 3 verts between your mesh islands before selecting your starting vert and running Zip Merge (via the 'M' menu).

LIMITATION: 
If you selected vertex is next to another border edge, Zip Merge will error. This is a current limitation of the addon as it operates based on expanding your selection, deselecting the original vertex, and merging the remaining selected border vertices in your selection. An easy fix is to add a temporary edge loop between your selected vertex and the border. Run Zip Merge, then delete the inserted edge loop.

Here is an illustration of what you need to avoid: