Effective September 1, 2021, the multiplayer service for the 2007 version of Age of Empires III: Complete Collection currently on Steam will no longer function. The critical factor driving this change is that the ESO domain on which this multiplayer service currently resides is no longer under Microsoft’s control and it will be repurposed by its new owners on that date. To continue accessing the multiplayer services: We have created a patch that points to a new backend owned by Microsoft that you must manually install prior to September 1, 2021.