TFS Attachement size 0KB via REST Call - tfs

Question

Whenever i tried to attach attachment with TFS WorkItem via REST call, attachment size is 0KB.
First I upload an attachment in Attachment Store using below code.
https://{instance}/DefaultCollection/_apis/wit/attachments?api-version=1.0&filename="{fileName}"
I send data in bytes array through rest call. and after this i attach that attachment with workitem.
Attaching attachment is success but size of an attachment is zero KB
Is there is an issue with TFS or something i am doing wrong?
I am using C# language for programming and REST Sharp for accessing VSTS APIs
Dim restClient = New RestClient("Server URL")
restClient.Authenticator = New HttpBasicAuthenticator("UserId", "Password")
Dim request = New RestRequest("API_Name", Method.POST)
request.AlwaysMultipartFormData = False
request.AddParameter(String.Format("{0}; charset=utf-8", contentType), File.ReadAllBytes(filePath), ParameterType.RequestBody)
request.RequestFormat = DataFormat.Json
Dim response As IRestResponse = restClient.Execute(request)
Return response
I am sending file data in bytes.
Attaching Attachment with WorkItem.
Dim restClient = New RestClient(ACCESS_URL)
restClient.Authenticator = New HttpBasicAuthenticator(USER_NAME, PASSWORD)
Dim request = New
RestRequest("CollectionName}/_apis/wit/workitems/{WorkItem_ID}", Method.PATCH)
request.AddParameter("application/json-patch+json; charset=utf-8",
"post_Data", ParameterType.RequestBody)
request.RequestFormat = DataFormat.Json
Dim response As IRestResponse = restClient.Execute(request)
Return response
Post_Data is an json string which take this type of data
[{
"op": "add",
"path": "/relations/-",
"value": {
"rel": "AttachedFile",
"url": "AttachementURI",
}]

Answer 1

You missed "attributes" section in the Post_Data, try with below:
[{
"op": "add",
"path": "/relations/-",
"value": {
"rel": "AttachedFile",
"url": "AttachementURI",
"attributes": {
}
}]

Answer 2

I can reproduce this issue when keep the { file-contents } as empty.
So, make sure you have specified the { file-contents }.
To attach a file to a work item, upload the attachment to the
attachment store, then attach it to the work item. See Add an attachment for details.
Upload an attachment:
POST https://{instance}/DefaultCollection/_apis/wit/attachments?api-version={version}&filename=Spec.txt
Content-Type: application/octet-stream
{ file-contents }
Add an attachment for specific work item:
PATCH https://fabrikam-fiber-inc.visualstudio.com/DefaultCollection/_apis/wit/workitems/299?api-version=1.0
Content-Type: application/json-patch+json
[
{
"op": "test",
"path": "/rev",
"value": 3
},
{
"op": "add",
"path": "/fields/System.History",
"value": "Adding the necessary spec"
},
{
"op": "add",
"path": "/relations/-",
"value": {
"rel": "AttachedFile",
"url": "https://fabrikam-fiber-inc.visualstudio.com/DefaultCollection/_apis/wit/attachments/098a279a-60b9-40a8-868b-b7fd00c0a439?fileName=Spec.txt",
"attributes": {
"comment": "Spec for the work"
}
}
}
]
See below C# sample to upload and add the attachment for a work item:
C# (UploadTextFile method)
C# (AddAttachment method)