To get SLA data (Target date and SLA status) via Jira API, you need to:
Enable Custom fields.
Click the “Update” button to update your SLA configuration.
When you have your goals for custom fields enabled, SLA data (SLA actual status і SLA Target date) will be recorded to the custom fields of issues. To get the id (key) of custom fields, click on the button shown below:
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You’ll get such a pop-up window with the ID of custom fields:
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