query MerchantCategories {
  merchantCategories {
    code
    description
  }
}

curl --request POST \
  --url https://api.sandbox.com/graphql \
  --header 'Content-Type: application/json' \
  --header 'Authorization: Bearer <YOUR_ACCESS_TOKEN>' \
  --data '{
  "query": "query MerchantCategories {\n  merchantCategories {\n    code\n    description\n  }\n}"
}'

{
  "data": {
    "merchantCategories": {
      "code": "example",
      "description": "example"
    }
  }
}