Attempt fix for #6261

freqtrade/optimize/backtesting.py

@@ -357,6 +357,15 @@ class Backtesting:
                     # use Open rate if open_rate > calculated sell rate
                     return sell_row[OPEN_IDX]
 
+                if (
+                    trade_dur == 0
+                    and trade.open_rate < sell_row[OPEN_IDX]  # trade-open > open_rate
+                    and sell_row[OPEN_IDX] > sell_row[CLOSE_IDX]  # Red candle
+                ):
+                    # ROI on opening candles with custom pricing can only
+                    # trigger if the entry was at Open or lower.
+                    # details: https: // github.com/freqtrade/freqtrade/issues/6261
+                    raise ValueError("Opening candle ROI on red candles.")
                 # Use the maximum between close_rate and low as we
                 # cannot sell outside of a candle.
                 # Applies when a new ROI setting comes in place and the whole candle is above that.
@@ -414,7 +423,10 @@ class Backtesting:
             trade.close_date = sell_candle_time
 
             trade_dur = int((trade.close_date_utc - trade.open_date_utc).total_seconds() // 60)
-            closerate = self._get_close_rate(sell_row, trade, sell, trade_dur)
+            try:
+                closerate = self._get_close_rate(sell_row, trade, sell, trade_dur)
+            except ValueError:
+                return None
             # call the custom exit price,with default value as previous closerate
             current_profit = trade.calc_profit_ratio(closerate)
             order_type = self.strategy.order_types['sell']