ftx: rewrite order cancel handling

pkg/exchange/ftx/exchange.go

@@ -2,6 +2,7 @@ package ftx
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 	"net/http"
 	"net/url"
@@ -560,18 +561,26 @@ func (e *Exchange) CancelOrders(ctx context.Context, orders ...types.Order) erro
 			logrus.WithError(err).Error("rate limit error")
 		}
 
+		var resp *ftxapi.APIResponse
+		var err error
 		if len(o.ClientOrderID) > 0 {
 			req := e.client.NewCancelOrderByClientOrderIdRequest(o.ClientOrderID)
-			_, err := req.Do(ctx)
-			if err != nil {
-				return err
-			}
+			resp, err = req.Do(ctx)
 		} else {
 			req := e.client.NewCancelOrderRequest(strconv.FormatUint(o.OrderID, 10))
-			_, err := req.Do(ctx)
+			resp, err = req.Do(ctx)
+		}
+
 		if err != nil {
 			return err
 		}
+
+		if !resp.Success {
+			v, err := unmarshalResult(resp.Result)
+			if err != nil {
+				return err
+			}
+			return fmt.Errorf("cancel order failed: %v", v)
 		}
 	}
 	return nil
@@ -655,3 +664,8 @@ func (e *Exchange) Transfer(ctx context.Context, coin string, size float64, dest
 	}
 	return resp.Result.String(), nil
 }
+
+func unmarshalResult(result json.RawMessage) (a interface{}, err error) {
+	err = json.Unmarshal(result, &a)
+	return a, err
+}