This could happen due to multiple reasons. Verify and confirm the following:
- Your ad unit, ad network, mediation group and line items are enabled.
- The appropriate ad network adapters are installed.
- Your mediation group geo targeting makes sense (for example, if you targeted the US and sent the request from Canada, geo targeting will not work).
- Your mediation line item has the correct mapping of ad network placements. Make sure the Placement ID is correct.
- The ad network placements don’t have a very high floor or a filtering/blocking rule.
- Your Ad Unit ID is correct in the game code. Even an extra space or character in game source code will result in an invalid request.
If you still encounter issues with using the Mediation SDK or the Unity Mediation platform, contact Unity Ads Support or the Unity Open Mediation team. For more information, see documentation on Unity Mediation.