If you are inside the map maker
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Go to the world tab, check the box that says "Has portal" and then write in coordinates of where you want the portal to be. You can see the coordinates in the bottom right corner if you fly around. Make sure you fill in all fields then save the map once again.
The next time you go into cape you will see a portal there, enter it and it should be your map.
You can also export the map and then give the exported files to others so they're able to test the map.
