Appointment+ Gcal integration sharing error

I'm attempting to add the gmail service account eMail to shared calendar settings. However even if I add the email and the ability to edit it adds only as the ability to see free/busy and the rest of the options are greyed out. So of course trying to do test errors out: [October 22, 2015 8:35 am] Insert went wrong: Error calling POST (403) Forbidden

Am I adding the wrong email? or is something else wrong.