curl --request POST \
  --url https://api.withsplendor.com/v1/ingest/sources/{source_key}/uploads/parts \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --header 'x-splendor-tenant-id: <x-splendor-tenant-id>' \
  --data '
{
  "part_numbers": [
    123
  ],
  "upload_session_id": "<string>"
}
'

{
  "parts": [
    {
      "expires_at": "2026-01-15T09:30:00Z",
      "part_number": 1,
      "upload_url": "https://acme-uploads.s3.amazonaws.com/..."
    }
  ]
}