If you see the following errors in your project, this means that the Unity Editor was not able to fetch your Game ID:
GameID not found
Warning, failed to retrieve GameID from Dashboard
The most common reason for these errors is because your Unity Dashboard project is not linked to the project inside the Editor.
To resolve this issue, in the Unity Editor, go to Edit > Project Settings > Services to check the status of your linked project. After your project is successfully linked, try building again.
For more information, see the Unity Mediation documentation.