...
If developer is external to Syensqo, request the creation of a Syensqo Account on Service One
Calendar Invitations
Depending on the responsibilities of the developer, think to add the account to the Daily / Sprint Planning / Sprint Review meetings.
JIRA
Once the account is created at Syensqo, request a license for that email address. Once the license has been provisioned, in the Jira Project Settings, navigate to people and add the account of the developer.
...