curl --request PATCH \
  --url https://api.example.com/api/v2/contact/{contact_id}/relationship/opportunities/{target_id} \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "through": {
    "role_name": "champion"
  }
}
'

{
  "parent": {
    "id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
    "record_type": "<string>"
  },
  "api_name": "<string>",
  "item": {
    "related_record_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
    "related_record_type": "<string>",
    "through": {
      "id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
      "record_type": "<string>",
      "attributes": {
        "is_primary": {
          "value": true,
          "value_type": "boolean"
        }
      }
    }
  }
}