After importing adding a project into Swanly roadmap, it's necessary to have the start and end dates assigned to the issues. Otherwise, the roadmap will display just the project list. Please, check the process to add start and end dates to the issues.
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Access Swanly via Apps > Swanly RoadmapRoadmaps
Choose the view issue roadmap you wish to work with - Release or Issue
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from the dropdown
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Click on the button + ADD ISSUE located on the hand-right in the top corner.
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After doing this process, you should be able to see the issues on the Swanly issue roadmap.