feat: improve docstring and error handling

part of #12206

freqtrade/data/dataprovider.py

@@ -577,7 +577,8 @@ class DataProvider:
         Warning: Performs a network request - so use with common sense.
         :param pair: Pair to get the data for
         :return: Funding rate dict from exchange or empty dict if funding rate is not available
-            If available, the "funding_rate" field will contain the funding rate.
+            If available, the "fundingRate" field will contain the funding rate.
+            "fundingTimestamp" and "fundingDatetime" will contain the next funding times.
             Actually filled fields may vary between exchanges.
         """
         if self._exchange is None:

freqtrade/exchange/exchange.py

@@ -2010,6 +2010,8 @@ class Exchange:
         Won't work for non-futures markets
         """
         try:
+            if pair not in self.markets or self.markets[pair].get("active", False) is False:
+                raise ExchangeError(f"Pair {pair} not available")
             return self._api.fetch_funding_rate(pair)
         except ccxt.NotSupported as e:
             raise OperationalException(