Classic ASP Requires Chilkat v11.0.0+
Xero Upload Attachment

Demonstrates how to upload an attachment to Xero.
Chilkat Classic ASP Downloads

Classic ASP
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body>
<%
success = 0

'  This example requires the Chilkat API to have been previously unlocked.
'  See Global Unlock Sample for sample code.

set http = Server.CreateObject("Chilkat.Http")

'  Important: Make sure your OAuth2 access token was obtained with the scope "accounting.attachments"
'  included in the list of scopes.

set jsonToken = Server.CreateObject("Chilkat.JsonObject")
success = jsonToken.LoadFile("qa_data/tokens/xero-access-token.json")
If (success = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( jsonToken.LastErrorText) & "</pre>"
    Response.End
End If

http.AuthToken = jsonToken.StringOf("access_token")

'  Replace the value here with an actual tenant ID obtained from this example:
'  Get Xero Tenant IDs
http.SetRequestHeader "Xero-tenant-id","83299b9e-5747-4a14-a18a-a6c94f824eb7"

http.Accept = "application/json"

url = "https://api.xero.com/api.xro/2.0/{$Endpoint}/{$Guid}/Attachments/{$Filename}"

'  Endpoint can be Invoices, Receipts, CreditNotes, PurchaseOrders, etc.
success = http.SetUrlVar("Endpoint","Invoices")

'  Guid is the ID of the item, such as the InvoiceID.
success = http.SetUrlVar("Guid","0032f627-3156-4d30-9b1c-4d3b994dc921")

'  Filename is the filename of the attachment you are uploading.
success = http.SetUrlVar("Filename","penguins.jpg")

'  Load the file to be uploaded (from the local filesystem).
set bd = Server.CreateObject("Chilkat.BinData")
success = bd.LoadFile("qa_data/jpg/penguins.jpg")
If (success = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( "Failed to load attachment file.") & "</pre>"
    Response.End
End If

'  Indicate the content-type according to the file content type.
'  Common content-types are:   image/jpg, image/png, application/pdf, application/zip, application/msword
'  If you don't know, use application/octet-stream
set resp = Server.CreateObject("Chilkat.HttpResponse")
success = http.HttpBd("POST",url,bd,"image/jpg",resp)
If (success = 0) Then
    Response.Write "<pre>" & Server.HTMLEncode( http.LastErrorText) & "</pre>"
    Response.End
End If

Response.Write "<pre>" & Server.HTMLEncode( "Response Status Code: " & resp.StatusCode) & "</pre>"

set jsonResponse = Server.CreateObject("Chilkat.JsonObject")
success = jsonResponse.Load(resp.BodyStr)
jsonResponse.EmitCompact = 0
Response.Write "<pre>" & Server.HTMLEncode( jsonResponse.Emit()) & "</pre>"

If (resp.StatusCode <> 200) Then
    Response.Write "<pre>" & Server.HTMLEncode( "Failed.") & "</pre>"
    Response.End
End If

'  A sample response:

'  Use this online tool to generate parsing code from sample JSON: 
'  Generate Parsing Code from JSON

'  {
'    "Id": "35333c64-4449-457b-bf6a-1b64d538e3c7",
'    "Status": "OK",
'    "ProviderName": "Chilkat2222",
'    "DateTimeUTC": "\/Date(1587212597758)\/",
'    "Attachments": [
'      {
'        "AttachmentID": "daf106e2-8634-4349-bfcc-86c1df0793b2",
'        "FileName": "penguins.jpg",
'        "Url": "https://api.xero.com/api.xro/2.0/Invoices/0032f627-3156-4d30-9b1c-4d3b994dc921/Attachments/penguins.jpg",
'        "MimeType": "image/jpg",
'        "ContentLength": 777835
'      }
'    ]
'  }

%>
</body>
</html>