Impossible to export my game

Hello, I come here to search for help, I followed a tutorial to create a multiplayer game
----> Blueprint Multiplayer: Project Overview | 01 | v4.11 Tutorial Series | Unreal Engine - YouTube

The problem is that when I try to export it, there is an error

I do not know what to do … Know that I managed in the comments of the tutorial to find a version of the project in 4.15 and the problem persists …

I also specify that my game includes Steam as this is also in the tutorial.

thank you