"Frida's Dilemma" - "Negotiations" [Campaign 1, Mission 4]

I can't enter the one-way portal, which is located slightly above the middle of the map. Perhaps this is related to the fact that after defeating the garrison, my castles and mines remained mine and did not go to the red player.

I don't quite understand, after defeating which garrison? I did it like this: first, I defeated the purple player on the right, cleared the entire territory up to the garrison, then approached the dwarf garrison, received their demands, and fulfilled them. After that, they let me pass through their garrisons. I ran to the castle, and after the cutscene, it turns out that while Frida wanted to resolve everything peacefully, Laslo attacks the dwarves. After this, two of my castles and all the mines go to Laslo, and Frida receives the task of escaping the dwarf territory. Then, you can say, we run straight ahead, killing monsters and joining friendly units. Along the way, you can manage to collect the set of artifacts of the dwarven royal armor and complete a couple of minor quests. One of the quests is very useful: kill the hydras guarding the mine. After completing the quest, the mine will serve as a kind of teleport. In general, in the end, we reach another garrison, which turns out to be empty. Behind it, we dive into the Dungeon, take a couple of steps - and the mission is completed.