POST to /services/data/vXX.0/composite with a JSON body containing a compositeRequest array
Each element in compositeRequest includes a method, url (relative), referenceId (unique string), and optionally a body
Reference the output of a prior subrequest in later subrequests using the @{referenceId.field} syntax
Set allOrNone to true if you want all subrequests rolled back when any single one fails
Parse the compositeResponse array in the response — each item has an httpStatusCode and a body
Known gotchas
A single composite request supports up to 25 subrequests; exceed this and the entire call is rejected
With allOrNone false, earlier successful subrequests are not rolled back even if a later one fails — handle partial success explicitly
Not all REST endpoints are supported as subrequests; query and tooling API calls have restrictions — check the documentation for the specific API version
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