I'm playing a second character now and have reached RA. But still I haven't been offered "DS9 Under Siege". When I approach DS9 I have an option to join the fleet action but doing so does not list it on the tab "In Progress". Does anyone else recognize this and can tell me what I should do to trigger this mission?
Joining the fleet action should instance you straight into it. It does not appear in your contact log. When you complete, it automatically credits you with completion and reward. If you leave the mission prematurely, it will be automatically dropped.