ADF Google Ads Linked Service using Service Authentication as the Authentication Type

We are trying to access Google Ads data using a Google Ads Service Account, and the ADF Google Ads Linked Service.  We have set the linked service "Authentication type" to be "Service authentication".    We generated a private key for this Service Account in Google, and we have used the key as the value in the "Private key" field of the linked service.  We have populated the other required linked service fields (Name, Client customer ID, Developer token, Email), and also the optional "Login customer ID" field.  We have also designated the linked service to use a self-hosted integration runtime instead of the AutoResolveIntegrationRuntime.  

When testing the connection, we are receiving this error message:

Test connection operation failed.
Failed to open the database connection.
Fail to read from Google Ads.
Parameter was empty
Parameter name: pkcs8PrivateKey

Does anyone in the Tech Community use this new version of the Google Ads linked service with the Authentication Type set to "Service authentication" instead of "User authentication"?

Does anyone have any insight about the error message we are receiving?