Hello,

steam workshop has trouble to support online hosting of scenarios from just subscribing to a mod. To host the game online you need to:

When subscribed, get this file:
C:\Program Files (x86)\Steam\steamapps\common\Age of Mythology\mods\Children of Memories RPG\scenario\ChiMem RPG by Tasterix.scx

Into this folder:
C:\Program Files (x86)\Steam\steamapps\common\Age of Mythology\scenario\