Create or update multiple students in a single request with partial success support. Each item is matched by either studentId (EduSign internal ID, update only) or externalReferenceId (create-or-update) — provide at most one. Providing both fails the item with STUDENT_IDENTIFIER_AMBIGUOUS; a studentId with no match fails with STUDENT_NOT_FOUND; items with neither identifier are treated as new records. Two items resolving to the same student (one by studentId, one by externalReferenceId) both fail with STUDENT_DUPLICATE_MATCH — reference each student at most once. Min 1, max 1000 students per request. Returns 200 when all items succeed, 207 for partial success with per-item failures. succeeded and failed are sorted ascending by inputIndex.

Per-item error codes: VALIDATION_ERROR, STUDENT_IDENTIFIER_AMBIGUOUS, STUDENT_NOT_FOUND, DUPLICATE_EXTERNAL_REFERENCE_ID, STUDENT_DUPLICATE_IN_REQUEST, STUDENT_DUPLICATE_MATCH, REQUIRED_FIELD_MISSING, EMAIL_REQUIRED_FOR_CREDENTIALS, EXTERNAL_REF_ID_REQUIRED_WITH_EXTERNAL_REFERENCE_TYPE, USERNAME_COLLISION, STUDENT_IS_ARCHIVED, CREATE_FAILED, UPDATE_FAILED.