Network problem: Please make sure your network connection is normal, and try to restart the router or adjust the network settings.

Steam server problem: Please check whether the Steam server is running normally. You can check the status of the server on the official website of Steam.

Firewall or antivirus software problem: Please check whether your firewall or antivirus software prevents the update of DOTA2. You can try to close them temporarily and restart Steam.

The game file is corrupted: Please try to verify the integrity of the game file. You can right-click DOTA2 in the Steam library, select Properties, and then click Verify the integrity of the game file in the Local Files tab.

If the above methods can't solve the problem, I suggest you contact Steam customer service or DOTA2 official customer service for help.