ASP classic POST multipart

I need to improve classic ASP code, which performs HTTP POST request, multipart with an attachment and payload information such as text and / or json.

The ASP code generates HTTP content to send to a REST service, but it is returning the message:
"The request content was malformed: Unexpected end of multipart entity "

/ **** Content sent with POST *** /
---------------- 010201080703010401070605
Content-Disposition: form-data; name = "className"

Acquirer
---------------- 010201080703010401070605
Content-Disposition: form-data; name = "properties"

{
"code": "2052776",
"amount_transaccion": 141.46,
"codigo_tipo_impresion": "2"
}
---------------- 010201080703010401070605
Content-Disposition: form-data; name = "file"; filename = "E: / data / Clientes / PMP / 05 digitalization project / scrlv / vouchers / SOP-2052776-0029-7225-237151-2.png"
Content-Type: image / png

(data)
---------------- 010201080703010401070605--