curl --request GET \
  --url https://mm-api.merchantspring.io/customGroups/{id} \
  --header 'x-api-key: <api-key>'

{
  "group": {
    "groupId": 123,
    "groupName": "<string>",
    "products": [
      {
        "sellerSku": "<string>"
      }
    ],
    "brands": [
      "<string>"
    ]
  }
}