You've made a game that requires people to join in order to play

[PCGamesRule]

First map is prologue, i.e. tutorial, second and third multiplayer.

Expect for popular battle royal games, or games like rust or scum where it's assumed you'll mostly fight against other people, I think the main interest in zombie shooters is solo with the OPTION of co-op, eg. dying light 1 and 2.

Often devs will use multiplayer as a way to avoid having to create competent AI enemies.
In your trailer, the enemy head straight toward you, weapons down and trot into the hail of gunfire you provide. Except for druggies/insane people, no one does that. They should have taken cover and returned fire.

I can see potential in your game assuming you can work out the kinks, but you might want to consider providing a solid single player offline mode FIRST, because without that, you'll get ignored by a significant group of potential buyers.

Good luck