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You can specify the webservice request body as shown below. If {worklog.<field>} is used, then OnLink will automatically pull all worklog entries, as each issue can have more than one worklog.
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The {worklog.author.accountId.getid('workspaceid', 'asset object name', 'atlassian user object name')} can be used to reverse map Jira User ID to Workday ID. This mapping is driven from JSM Assets object that maps Jira User to Workday ID. Note that the Workday ID field should be the label on the object. To get the Workspace ID, you can run this URL: https://yourinstancename.atlassian.net/rest/servicedeskapi/assets/workspace