How to send raw JSON data with a post request using mechanize in python

I am trying to POST JSON data to a api using a python script. I'm using python 2 and mechanize package.

import mechanize
import json, logging, sys, urllib

br = mechanize.Browser()
url = 'url_here'
headers = [('User-Agent', 'Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:60.0) Gecko/20100101 Firefox/60.0'),
('Content-Type', 'application/json')]
br.set_handle_robots(False)
br.set_debug_responses(True)
br.set_debug_redirects(True)
br.set_debug_http(True)
logger = logging.getLogger("mechanize")
logger.addHandler(logging.StreamHandler(sys.stdout))
logger.setLevel(logging.INFO)
body = {"audience":{"name":"asd","criteria":[{"category":"common","label":"Industry","tags":[{"tag":"Information Technology","text":"Information Technology","score":2,"type":"Similar"},{"tag":"Computer Software","text":"Computer Software","score":2,"type":"Similar"},{"tag":"Marketing and Advertising","text":"Marketing and Advertising","score":2,"type":"Similar"}],"type":"input-group","icon":"restaurant_menu","operation":"include","suggestions":True,"related":False,"multiple":True,"rankings":True,"showStrictness":True,"strict":False,"stub":{"tags":[],"values":[]},"values":["Information Technology","Computer Software","Marketing and Advertising"],"field":"industry","scope":"companies"},{"category":"common","label":"Contact Location","type":"location-group","icon":"person_pin_circle","operation":"include","multiple":True,"suggestions":True,"related":False,"tip":"Find people based on their location. You can filter by Country, and Region / City (for example, San Francisco Bay Area).","options":[{"value":"country","label":"Country","placeholder":"e.g... United States, Australia"},{"value":"locality","label":"Region / City","placeholder":"e.g... San Francisco, Toronto"}],"stub":{"tags":[],"values":[]},"tags":[],"values":["India","United States of America","United Kingdom"],"field":"country","childField":"country","scope":"contacts"},{"category":"tech","label":"Technology Used","type":"input-group","operation":"include","suggestions":True,"related":False,"icon":"power","multiple":True,"rankings":True,"placeholder":"e.g... Salesforce, jQuery, Ruby","tip":"Find companies based on specific web-based technologies they use. Note: This filter will narrow your search significantly. Any companies that dont use the technology you enter will be excluded from the results. ","stub":{"tags":[],"values":[]},"tags":[{"tag":"jQuery","text":"jQuery","score":2,"type":"Similar"},{"tag":"Angular JS v2","text":"Angular JS v2","score":0,"type":"Similar"}],"values":["jQuery","Angular JS v2"],"field":"technology","scope":"companies"}],"purchasedLeads":0,"estimatedReach":0,"maxLeadsPerCompany":3,"searchLeadCount":500,"emailGuesserScope":"professional"}}
br.addheaders = headers
response = br.open(url, data=json.dumps(body))
print response

But I am unable to send the JSON data successfully. But when I'm sending the data using urllib.urlencode() then the data is being sent but not being processed in the server as the server is expecting JSON data through the post request. Please someone help with this.