Why am I unable to start the next main story mission in Fortnite Save the World?

Save the World main story missions in Fortnite must be completed in order. If a the current active mission hasn't been completed, the next one cannot be started.

If you have completed the a main story quest, but get an "You don't have this mission yet" error when starting the next quest, try starting a different mission  or restarting Fortnite to sync your mission progress.