David!
That Bitfinex v2 endpoint is actually meant to be accessed via HTTP GET, not POST.
The params should be appended to the URL query like so:
https://api.bitfinex.com/v2/candles/trade:5m:tBTCUSD/hist?start=1434764470000&end=1497922870000
Also, you should be more specific on what you mean by the right data. If you don't get the answer at all - it may be due to a malformed request. If the prices are not corresponding to what you expect for requested period of history - you may want to ensure your timestamps are UTC time.
If you don't pass start and end filters in the HTTP GET URL querystring, you always get last 100 candles, as if there was no start/end filtering at all.
import requests
url = 'https://api.bitfinex.com/v2/candles/trade:5m:tBTCUSD/hist'
params = { 'start': 1434764470000, 'end': 1497922870000 }
r = requests.get(url, params = params)
data = r.json()
print(data)