Create a new offer on an existing application. application_id is required; starts_on and custom_fields (compensation components plus any offer custom fields configured on the hiring plan) are optional. The new offer is created with status=Created at version=1. If the application already has an offer, the submission is applied to the same offer chain rather than creating a competing record: a new version is created — and the prior version marked Deprecated — only when a version-triggering field changes, namely starts_on (when your organization enables offer versioning on start-date changes) or a compensation/offer custom field configured to trigger a new version; otherwise the current offer is updated in place. Approval flows configured for the hiring plan are attached automatically — partners must drive the approval through /v3/approval_flows before the offer can be sent to the candidate.