How can I replace legacy code URL for Poloniex API when tring to get data from BTC/XMR crypto pair?

Question

So, I'm trying to learn Python and wanted to request some cryptocurrency pair data from Poloniex API by using this code below, and as I understood correctly I referred to the legacy code that isn't supported anymore, so I'm kinda stuck with undefined URL that I have to find out myself in order to practically replace this old version of it and to make it work as it intended to.

Here is my code:

    import requests
    import json
    req = requests.get("https://poloniex.com/public?command=returnChartData&currencyPair=BTC_XMR&start=1546300800&end=1546646400&period=14400")
    json_obj = json.loads(req.text)
    for day in json_obj:
     print(day["close"])

It returns me these errors:

JSONDecodeError                           Traceback (most recent call last)
<ipython-input-87-3354a61008d7> in <cell line: 5>()
      3 import json
      4 req = requests.get("https://poloniex.com/public?command=returnChartData&currencyPair=BTC_XMR&start=1546300800&end=1546646400&period=14400")
----> 5 json_obj = json.loads(req.text)
      6 for day in json_obj:
      7  print(day["close"])

2 frames
/usr/lib/python3.10/json/decoder.py in raw_decode(self, s, idx)
    353             obj, end = self.scan_once(s, idx)
    354         except StopIteration as err:
--> 355             raise JSONDecodeError("Expecting value", s, err.value) from None
    356         return obj, end

JSONDecodeError: Expecting value: line 1 column 1 (char 0)