Have you registered this feature?
Before you begin, you must register it through PowerShell. Also keep in mind it is a preview feature (have a look at this page).
Register-AzProviderFeature -FeatureName CrossRegionRestore -ProviderNamespace Microsoft.RecoveryServices
FeatureName ProviderName RegistrationState
----------- ------------ -----------------
CrossRegionRestore Microsoft.RecoveryServices Registering
It might take up to 48 hours, you can check status.
Get-AzProviderFeature -FeatureName CrossRegionRestore -ProviderNamespace Microsoft.RecoveryServices
FeatureName ProviderName RegistrationState
----------- ------------ -----------------
CrossRegionRestore Microsoft.RecoveryServices Registered