Update a Contentful post using PUT request via Postman

I'm trying to update a Contentful entry using Postman.

What I did:

• In Contentful space, I created a test post to play with.
• Went to Settings - API Keys - Content management tokens and generated a Personal access token
• Created a GET request in Postman, passing space ID, master environment, and ID of the test post:

https://cdn.contentful.com/spaces/{spaceID}i/environments/master/entries?sys.id={postID} I also sent authorisation header with content delivery token.

The GET request goes successfully and I'm able to copy the JSON object-response.

{
  "sys": {
  "type": "Array"
},
  "total": 1,
  "skip": 0,
  "limit": 100,
  "items": [
  {
    "metadata": {
      "tags": []
    },
    "sys": {
      "space": {
        "sys": {
          "type": "Link",
          "linkType": "Space",
          "id": "d9r4mg123x4v"
        }
      },
      "id": "2Fwow39hxxx1bvMkjpsyV9",
      "type": "Entry",
      "createdAt": "2021-11-10T14:00:11.935Z",
      "updatedAt": "2021-11-10T14:06:51.393Z",
      "environment": {
        "sys": {
          "id": "master",
          "type": "Link",
          "linkType": "Environment"
        }
      },
      "revision": 3,
      "contentType": {
        "sys": {
          "type": "Link",
          "linkType": "ContentType",
          "id": "hotelInfo"
        }
      },
      "locale": "en-US"
    },
    "fields": {
      "name": "Test entry",
      "slug": "test-entry",
      "address": "Lviv",
      "cityName": "Lviv",
      "phone": "+380931231212",
      "coordinates": {
        "lon": -115.302,
        "lat": 36.18709
      },
      "dog": "100",
      "cat": "100",
      "delivery": "100",
      "photo": [
        {
          "sys": {
            "type": "Link",
            "linkType": "Asset",
            "id": "2hSnYhQDJzU99NvlsYdk3k"
          }
        }
      ],
      "additionalInfo": {
        "data": {},
        "content": [
          {
            "data": {},
            "content": [
              {
                "data": {},
                "marks": [],
                "value": "Test",
                "nodeType": "text"
              }
            ],
            "nodeType": "paragraph"
          }
        ],
        "nodeType": "document"
      },
      "featuredHotel": true,
      "phoneClicks": 1
    }
  }
],
  "includes": {
  "Asset": [
    {
      "metadata": {
        "tags": []
      },
      "sys": {
        "space": {
          "sys": {
            "type": "Link",
            "linkType": "Space",
            "id": "d9r4mg123x4v"
          }
        },
        "id": "2hSnYhQDJzU99NvlsYdk3k",
        "type": "Asset",
        "createdAt": "2021-11-10T13:59:59.954Z",
        "updatedAt": "2021-11-10T13:59:59.954Z",
        "environment": {
          "sys": {
            "id": "master",
            "type": "Link",
            "linkType": "Environment"
          }
        },
        "revision": 1,
        "locale": "en-US"
      },
      "fields": {
        "title": "JS",
        "description": "Lorem Ipsum",
        "file": {
          "url": "//images.ctfassets.net/d9r4mg123x4v/2hSnYhQDJzU99NvlsYdk3k/6fbabc7be7f4b28dc8b7deadd9892205/JS.png",
          "details": {
            "size": 23078,
            "image": {
              "width": 1024,
              "height": 1024
            }
          },
          "fileName": "JS.png",
          "contentType": "image/png"
        }
      }
    }
  ]
}
}

Now I want to create PUT request to send the updated JSON to the Contentful. I paste the JSON I got as a response from GET request. I change one of the values:

"name": "Test entry" to "name": "Test entry 123"

I send PUT request to https://api.contentful.com/spaces/{spaceID}/environments/master/entries/{postID}

The Authorisation header contains the Personal access token I generated before. The X-Contentful-Version header contains the version of the post, can be found in post details

When I send this request, I get JSON response with an empty "fields": {}

{
  "metadata": {
  "tags": []
},
  "sys": {
  "space": {
    "sys": {
      "type": "Link",
        "linkType": "Space",
        "id": "d9r4mg123x4v"
    }
  },
  "id": "2Fwow39hxxx1bvMkjpsyV9",
    "type": "Entry",
    "createdAt": "2021-11-10T13:57:10.882Z",
    "updatedAt": "2021-11-11T10:58:39.480Z",
    "environment": {
    "sys": {
      "id": "master",
        "type": "Link",
        "linkType": "Environment"
    }
  },
  "publishedVersion": 13,
    "publishedAt": "2021-11-10T14:06:51.393Z",
    "firstPublishedAt": "2021-11-10T14:00:11.935Z",
    "createdBy": {
    "sys": {
      "type": "Link",
        "linkType": "User",
        "id": "4123123123zOn3MkhuVB"
    }
  },
  "updatedBy": {
    "sys": {
      "type": "Link",
        "linkType": "User",
        "id": "4123123123zOn3MkhuVB"
    }
  },
  "publishedCounter": 3,
    "version": 23,
    "publishedBy": {
    "sys": {
      "type": "Link",
        "linkType": "User",
        "id": "4123123123zOn3MkhuVB"
    }
  },
  "contentType": {
    "sys": {
      "type": "Link",
        "linkType": "ContentType",
        "id": "hotelInfo"
    }
  }
},
  "fields": {}
}

And in Contentful Admin area, all the fields of the post become empty.

Contentful documentation says:

Contentful doesn't merge changes made to content, so when updating content, you need to send the entire body of an entry. If you update content with a subset of properties, you will lose all existing properties not included in that update.

You should always update resources in the following order:

• Fetch current resource.
• Make changes to the current resource.
• Update the resource by passing the changed resource along with current version number.

This way no unseen changes are overridden and unexpected conflicts are unlikely to occur.

Note: You can't update any of the sys property fields, including sys.id.

...so, I guess, I'm doing everything right - taking the post, editing data and sending updated post back. I tried editing my JSON data to send it without sys fields, but no luck. I'm stuck, anyone has any ideas what should I proceed with?