5) You must also share the agenda (all permissions) with the service account user/email (created at step 2): For this, go into Google calendar, choose "
Parameters" then tab "Agendas" (direct access with this link https://www.google.com/calendar/render?tab=mc#i). Click on link " Share parameters" at end of line of the Agenda to synchronize (It must be same Agenda than the one chosen on parameter "ID Agenda" at step 1). Then add the service account user into the email field, choose permission " Edit events" and validate by clicking " Add user".
With Google Apps for work (not required for standard gmail account), permissions may be forced to "Ready only" instead of "Edit". To solve this, go onto