curl --request POST \
  --url https://clarus-api.com/api/mapping_groups/{mapping_group_id}/mapping_group_fields \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --header 'X-Clarus-Subdomain: <api-key>' \
  --data '
{
  "data": {
    "type": "mapping_group_fields",
    "attributes": {
      "field_name": "sku",
      "field_type": "string"
    }
  }
}
'

import requests

url = "https://clarus-api.com/api/mapping_groups/{mapping_group_id}/mapping_group_fields"

payload = { "data": {
        "type": "mapping_group_fields",
        "attributes": {
            "field_name": "sku",
            "field_type": "string"
        }
    } }
headers = {
    "Authorization": "Bearer <token>",
    "X-Clarus-Subdomain": "<api-key>",
    "Content-Type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.text)

const options = {
  method: 'POST',
  headers: {
    Authorization: 'Bearer <token>',
    'X-Clarus-Subdomain': '<api-key>',
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({
    data: {
      type: 'mapping_group_fields',
      attributes: {field_name: 'sku', field_type: 'string'}
    }
  })
};

fetch('https://clarus-api.com/api/mapping_groups/{mapping_group_id}/mapping_group_fields', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

{
  "id": 210,
  "field_name": "sku",
  "field_type": "string",
  "mapping_group_id": 88
}

{
  "error": "<string>"
}

{
  "errors": [
    {
      "code": 123,
      "symbol": "<string>",
      "details": "<string>",
      "source": "<string>",
      "context": {}
    }
  ]
}