Submit an App Store version for App Review using the modern reviewSubmissions and reviewSubmissionItems endpoints, then poll or cancel it

Documented steps

1. Create a review submission: POST https://api.appstoreconnect.apple.com/v1/reviewSubmissions with body {"data":{"type":"reviewSubmissions","attributes":{"platform":"IOS"},"relationships":{"app":{"data":{"type":"apps","id":"<appId>"}}}}}
2. The platform attribute became optional as of API 1.7 (it can be inferred), but passing it explicitly is safest.
3. On 201, data.id is the reviewSubmission ID and data.attributes.state starts at READY_FOR_REVIEW.
4. Attach the version as a submission item: POST https://api.appstoreconnect.apple.com/v1/reviewSubmissionItems with body {"data":{"type":"reviewSubmissionItems","relationships":{"reviewSubmission":{"data":{"type":"reviewSubmissions","id":"<reviewSubmissionId>"}},"appStoreVersion":{"data":{"type":"appStoreVersions","id":"<appStoreVersionId>"}}}}}
5. reviewSubmissionItems can also reference appStoreVersionExperiment(V2), appCustomProductPageVersion, appEvent, inAppPurchaseVersion, subscriptionVersion, subscriptionGroupVersion, backgroundAssetVersion and gameCenter* versions. A plain app-version submission needs only the appStoreVersion relationship.
6. Submit for review: PATCH https://api.appstoreconnect.apple.com/v1/reviewSubmissions/{id} with body {"data":{"type":"reviewSubmissions","id":"<id>","attributes":{"submitted":true}}}
7. Poll with GET /v1/reviewSubmissions/{id}. The state enum is READY_FOR_REVIEW, WAITING_FOR_REVIEW, IN_REVIEW, UNRESOLVED_ISSUES, CANCELING, COMPLETING, COMPLETE.
8. To cancel before review finishes, PATCH the same endpoint with {"data":{"type":"reviewSubmissions","id":"<id>","attributes":{"canceled":true}}}
9. Once state reaches COMPLETE, read the underlying version's appVersionState for the outcome — e.g. PENDING_DEVELOPER_RELEASE, PENDING_APPLE_RELEASE, READY_FOR_DISTRIBUTION, REJECTED, METADATA_REJECTED.
10. Official docs: https://developer.apple.com/documentation/appstoreconnectapi/review-submissions | https://developer.apple.com/documentation/appstoreconnectapi/post-v1-reviewsubmissions | https://developer.apple.com/documentation/appstoreconnectapi/post-v1-reviewsubmissionitems | https://developer.apple.com/documentation/appstoreconnectapi/patch-v1-reviewsubmissions-_id_