CocoaPods problem when building iOS project with Google Ads

Hello,

My project works fine for android, but I just cannot build for iOS. When I try, gives below error in Google Mobile Ads files. What may be the reason, please help. (By the way I tried reinstalling iOS Support, doesn't work)

Executing which argument: pod
UnityEngine.Debug:Log(Object)
GoogleMobileAds.CocoaPodHelper:ExecuteCommand(String, String, String) (at Assets/GoogleMobileAds/Editor/CocoaPodHelper.cs:47)
GoogleMobileAds.CocoaPodHelper:Update(String) (at Assets/GoogleMobileAds/Editor/CocoaPodHelper.cs:16)
GoogleMobileAds.Postprocessor:runPodUpdate(String) (at Assets/GoogleMobileAds/Editor/PostProcessor.cs:44)
GoogleMobileAds.Postprocessor:OnPostprocessBuild(BuildTarget, String) (at Assets/GoogleMobileAds/Editor/PostProcessor.cs:27)
UnityEditor.HostView:OnGUI()

Could not create a new Xcode project with CocoaPods: Encountered unexpected error while running pod
UnityEngine.Debug:Log(Object)
GoogleMobileAds.Postprocessor:runPodUpdate(String) (at Assets/GoogleMobileAds/Editor/PostProcessor.cs:48)
GoogleMobileAds.Postprocessor:OnPostprocessBuild(BuildTarget, String) (at Assets/GoogleMobileAds/Editor/PostProcessor.cs:27)
UnityEditor.HostView:OnGUI()