Question to all who are playing Fortnite Save the World - why is my main mission suspended or why can't I play them (see picture)?

Question to all who are playing Fortnite Save the World - why is my main mission suspended or why can't I play them (see picture)?

Quite simply you are not strong enough

You have to level your heroes and your defenders first.

OK

Where can one level up his defenders?

You go in saving the world: Central → Survivors → Manage → Choose a good one and level it

You see how that works