diff --git a/relay/handlers/req.go b/relay/handlers/req.go
index 75edfa1..fd4fd39 100644
--- a/relay/handlers/req.go
+++ b/relay/handlers/req.go
@@ -19,12 +19,14 @@ var subscriptions = make(map[string]relay.Subscription)
 func HandleReq(ws *websocket.Conn, message []interface{}) {
 	if len(message) < 3 {
 		fmt.Println("Invalid REQ message format")
+		SendClosed(ws, "", "invalid: invalid REQ message format")
 		return
 	}
 
 	subID, ok := message[1].(string)
 	if !ok {
 		fmt.Println("Invalid subscription ID format")
+		SendClosed(ws, "", "invalid: invalid subscription ID format")
 		return
 	}
 
@@ -33,6 +35,7 @@ func HandleReq(ws *websocket.Conn, message []interface{}) {
 		filterData, ok := filter.(map[string]interface{})
 		if !ok {
 			fmt.Println("Invalid filter format")
+			SendClosed(ws, subID, "invalid: invalid filter format")
 			return
 		}
 
@@ -48,6 +51,12 @@ func HandleReq(ws *websocket.Conn, message []interface{}) {
 		filters[i] = f
 	}
 
+	// Check if subscription already exists
+	if _, exists := subscriptions[subID]; exists {
+		SendClosed(ws, subID, "duplicate: subID already opened")
+		return
+	}
+
 	subscriptions[subID] = relay.Subscription{ID: subID, Filters: filters}
 	fmt.Println("Subscription added:", subID)
 
@@ -55,6 +64,7 @@ func HandleReq(ws *websocket.Conn, message []interface{}) {
 	queriedEvents, err := QueryEvents(filters, db.GetClient(), "grain")
 	if err != nil {
 		fmt.Println("Error querying events:", err)
+		SendClosed(ws, subID, "error: could not query events")
 		return
 	}
 
@@ -64,6 +74,7 @@ func HandleReq(ws *websocket.Conn, message []interface{}) {
 		err = websocket.Message.Send(ws, string(msgBytes))
 		if err != nil {
 			fmt.Println("Error sending event:", err)
+			SendClosed(ws, subID, "error: could not send event")
 			return
 		}
 	}
@@ -74,6 +85,7 @@ func HandleReq(ws *websocket.Conn, message []interface{}) {
 	err = websocket.Message.Send(ws, string(eoseBytes))
 	if err != nil {
 		fmt.Println("Error sending EOSE:", err)
+		SendClosed(ws, subID, "error: could not send EOSE")
 		return
 	}
 }
@@ -141,3 +153,9 @@ func QueryEvents(filters []relay.Filter, client *mongo.Client, databaseName stri
 
 	return results, nil
 }
+
+func SendClosed(ws *websocket.Conn, subID string, message string) {
+	closeMsg := []interface{}{"CLOSED", subID, message}
+	closeBytes, _ := json.Marshal(closeMsg)
+	websocket.Message.Send(ws, string(closeBytes))
+}