I believe that relates to the larger mission of completing Season 3 as a whole. You’ll notice above the “Go” button a countdown to when the new provinces become available. Once they do, the mission will advance.
Not the same question Guv’nor,. They were saying that they did not have the mission. I have it. I have completed it. It just does not recognize that I have completed it.
I think most of the answer would be that this is not a “mission” in the true sense, and, if it was, completion would be when you finish all of season 3.
I’m not sure why the devs list it as a mission, but it is more a tracker of your progress. The real s3 mission is the one right after it that gives you a reward for completing all of season 3.
Hilariously, it IS the same question (and Rook rightfully merged it). Because my other alliance members were confused in the same way you are regarding it.
I passed over the topmost mission twice when looking because I’m so used to seeing a useless tracking mission there.
And that’s all it is. There’s no reward for it. It’s just another way to get to the next map for you. Which, in this case, it cannot do for another 18 or so days.