import requests
import json

client_id = '*******************************************************************'
secret = '***************************************************************'

r = requests.post('https://api.sandbox.paypal.com/v1/oauth2/token', auth = (client_id, secret), headers = {'Accept': 'application/json', 'Accept-Language': 'en_US'}, data = {'grant_type': 'client_credentials'})

token = r.json()['access_token']

s = """{
  "intent": "sale",
  "payer": {
    "payment_method": "credit_card",
    "funding_instruments": [
      {
        "credit_card": {
          "number": "**********************",
          "type": "visa",
          "expire_month": *,
          "expire_year": ****,
          "cvv2": ***,
          "first_name": "John",
          "last_name": "Doe"
        }
      }
    ]
  },
  "transactions": [
    {
      "amount": {
        "total": "7.47",
        "currency": "USD"
      },
      "description": "Test payment from API."
    }
  ]
}"""

post_data = json.loads(s)

r2 = requests.post('https://api.sandbox.paypal.com/v1/payments/payment', headers = {'Content-Type': 'application/json', 'Authorization': 'Bearer ' + token}, data = post_data)

In [10]: r2.status_code
Out[10]: 400

In [11]: r2.text
Out[11]: u'{"name":"MALFORMED_REQUEST","message":"The request JSON is not well formed.","information_link":"https://developer.paypal.com/webapps/developer/docs/api/#MALFORMED_REQUEST","debug_id":"************"}'