If you encounter a “MissingMethodException” error when using the Unity Ads Asset Package in Unity 2017.x, you likely need to update the API. Do so using one of the following methods. Option 1: In the Unity Editor, select Assets > Run API Updater to initiate the update (if this item is not available, see Option 3). Option 2: Right-click the target folder in the Project window, then select Run API Updater... to initiate the update (if this item is not available, see Option 3). Option 3: In the Editor, select Help > Search, then enter “api” in the search field. Next, select Run API Updater... from the results to run the update. Option 4: Quit Unity, and locate your Project file in the system directory. Delete the “Library” folder, then reopen the Project in Unity to trigger an API Update Required prompt. Select I Made a Backup, Go Ahead! to run the update. If none of these methods resolve the issue, please contact support.