import requests

url = "http://mockbin.com/har"

payload = "{\"number\":1,\"string\":\"f\\\"oo\",\"arr\":[1,2,3],\"nested\":{\"a\":\"b\"},\"arr_mix\":[1,\"a\",{\"arr_mix_nested\":{}}],\"boolean\":false}"
headers = {'content-type': 'application/json'}

response = requests.request("POST", url, data=payload, headers=headers)

print(response.text)