curl --request POST \
  --url https://services.leadconnectorhq.com/locations/{locationId}/customFields/upload \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: multipart/form-data' \
  --header 'Version: <version>' \
  --form id=aWdODOBVOlH1RUFKWQke \
  --form maxFiles=15

{
  "uploadedFiles": {
    "FileName.csv": "https://highlevel-private-staging.storage.googleapis.com/location/Ar4JQgIyuzRsVuwD9RSK/custom-Field/UpZLmohmKEQYn0ymqplY/56e0d7fc-085c-4a07-9e1d-6d8fdac7e710.csv"
  },
  "meta": [
    {
      "fieldname": "FileName.csv",
      "originalname": "FileName.csv",
      "encoding": "7bit",
      "mimetype": "text/csv",
      "size": 2061,
      "url": "https://highlevel-private-staging.storage.googleapis.com/location/Ar4JQgIyuzRsVuwD9RSK/custom-Field/UpZLmohmKEQYn0ymqplY/56e0d7fc-085c-4a07-9e1d-6d8fdac7e710.csv"
    }
  ]
}