Send file using Axios Assyst REST API - rest

Question

Working in Blue Prism .Net environment utilising the HTTP utility to make calls to Axios Assyst (an IT service desk 3rd party software).
My HTTP request is as per below:
POST /assystREST/v2/site/10/attachments/binary HTTP/1.1
Host: <myserver>:<myport>
Content-Type: multipart/form-data; boundary=----WebKitFormBoundary<base64 encode here>
Accept: application/json
Authorization: Basic <base64 encoded key>
{
"eventId": 10010045,
"fileName": "C:\Users\Me\Desktop\MyFile.msg",
"attachment": "data:;base64,<base64 encoded file>
"onBehalfOfUser": "MR ROBOT",
"custom": {},
"attachedByUserId": <my ID>,
"name": "C:\Users\Me\Desktop\MyFile.msg",
"event":{
"assystRESTType": "event",
"assystRESTXMLType": "eventDto",
"id": 10010045
},
"attachedByUser":{
"assystRESTType": "assystUser",
"assystRESTXMLType": "assystUserDto",
"name": "Mr Robot - Test",
"id": <my ID>,
"shortCode": "MR ROBOT"
}
}
I can create and close my tickets but unable to send/save files to my newly created tickets. I get a HTTP STATUS CODE 410-GONE and the below exception JSON response:
{
"type": "NotFoundException",
"message": "The requested resource is not available.",
"messageKey": "rest.exceptions.NotFoundException",
"diagnostic": "Could not find resource for relative : /site/10/attachments/binary of full path: http://server:port/assystREST/v2/site/10/attachments/binary"
}
I'm following the instructions and guidelines noted in the official Axios Assyst Web Service wiki(per the below link), i.e. I'm using multipart/form-data while sending the file, a .msg file, and the binary of said file (yes I know this adds 33% more to the file size): https://wiki.axiossystems.com/assyst10SP75Wiki/index.php/Integrations:assystREST#Attachments
My issue is that 400 status codes would denote an issue on the client side but I've checked internally re firewall/port being used and nothing is being blocked.
I've reasearched 410 status codes and it would seem that the issue is server side but one that the server is not willing to elaborate on.
For testing I'm using Postman as it allows for greater flexibility rather than using Blue Prism, the JSON response is the same.
Looking for some guidance re status code 410 and possible solutions, note I've limited scope re options due to Blue Prisms .net vbo's.