const options = {
  method: 'POST',
  headers: {'X-Spree-Seller-Id': '<x-spree-seller-id>', Authorization: 'Bearer <token>'}
};

fetch('http://{defaultHost}/api/v3/seller/onboarding/submit_for_review', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

curl --request POST \
  --url http://{defaultHost}/api/v3/seller/onboarding/submit_for_review \
  --header 'Authorization: Bearer <token>' \
  --header 'X-Spree-Seller-Id: <x-spree-seller-id>'

{
  "status": "ready_for_review",
  "progress": {
    "done": 0,
    "total": 0
  },
  "requirements": []
}

{
  "error": {
    "code": "processing_error",
    "message": "Requirements Accept terms is not complete"
  }
}