Power BI upload action not working

We are trying to upload a file using powerBI import API. But it keeps throwing 400 Bad request
with the below responseResponse

{
  "error": {
    "code":"UnknownError",
    "pbi.error": {
      "code":"UnknownError",
      "parameters":{},
      "details":[],
      "exceptionCulprit":1
    }
  }
}

API referred: https://docs.microsoft.com/en-us/rest/api/power-bi/imports/postimport
The following is my request.

URL: https://api.powerbi.com/v1.0/myorg/imports?datasetDisplayName=demo
Header: Authorization: Bearer <token>, Content-Type: multipart/form-data; boundary=JLQPFBPUP0
Body:
--JLQPFBPUP0
Content-Disposition: form-data; name=model.csv; filename=model.csv;
Content-Type: text/csv
name,age
John,12
--JLQPFBPUP0--

Code:

require 'rest-client'

url = https://api.powerbi.com/v1.0/myorg/imports?datasetDisplayName=demo
payload = "--JLQPFBPUP0
           Content-Disposition: form-data; name=model.csv; filename=model.csv;
           Content-Type: text/csv
           name,age
           John,12
           --JLQPFBPUP0--"

RestClient.post(url, payload, :authorization => "Bearer <token>", :content_type => "multipart/form-data; boundary=JLQPFBPUP0")