I have been trying to insert a Google calendar event via Google service account that was created for an app in my dev console, but I am continually getting a helpless 404 re
I had the same problem. The solution was to add an email client, whose calendar event you want to send.
Credential = new ServiceAccountCredential(
new ServiceAccountCredential.Initializer(serviceAccountEmail)
{
Scopes = Scopes,
User = "example_client_email@gmail.com"
}.FromCertificate(certificate));