curl --request PUT \
  --url https://api.example.com/api/DocumentTemplates/Custom-Fields \
  --header 'Content-Type: application/json' \
  --data '
{
  "fields": [
    {
      "id": 123,
      "customerID": 123,
      "name": "<string>",
      "slug": "<string>",
      "formula": "<string>"
    }
  ],
  "deleteIds": [
    123
  ]
}
'

[
  {
    "id": 123,
    "companyID": 123,
    "name": "<string>"
  }
]