Unity Ads not appearing on Mobile Build

Unity Services
,
1

I’ve applied Unity Ads on my build and it works fine on the engine through PC. (both banner ads and rewarded ads)
But once I build it to my mobile test device, ads does not seem to appear with the following error log:

Error loading Ad Unit Rewarded_Android: INVALID_ARGUMENT - adMarkup is missing
UnityEngine.Logger:Log(LogType, Object)
RewardedAdsButton:OnUnityAdsFailedToLoad(String, UnityAdsLoadError, String)
UnityEngine.Advertisements.Utilities.CoroutineExecutor:Update()

  1. I’ve checked the ad has initizlized.
  2. The placement ID is valid.
  3. It prints “Loading Ad: Rewarded_Android” right before the error

What could be the issue?
Thanks in advance.