Send Push Notification - It shows successful response but not showing any notifcation - go

Question

I was trying to send push notification through fcm. In the response, I get all successful response. But I didn't get any notification. In other way, I tried to send notification directly from firebase console, and I get the notfication with the same token. So, I don't know what is the bug in this code. Token is okay. Response is also OK. but after executing code, I don't get any notification.
package main
import (
"context"
"encoding/base64"
"log"
"server/config"
db "server/database"
firebase "firebase.google.com/go/v4"
"firebase.google.com/go/v4/messaging"
"github.com/gin-gonic/gin"
"google.golang.org/api/option"
)
func init() {
config.Init()
db.ConnectRedis()
}
var ctx = context.Background()
func getDecodedFireBaseKey() ([]byte, error) {
fireBaseAuthKey := config.Env.FirebaseAuthKey
decodedKey, err := base64.StdEncoding.DecodeString(fireBaseAuthKey)
if err != nil {
return nil, err
}
return decodedKey, nil
}
func SendPushNotification(deviceTokens []string) error {
decodedKey, err := getDecodedFireBaseKey()
if err != nil {
return err
}
opts := []option.ClientOption{option.WithCredentialsJSON(decodedKey)}
app, err := firebase.NewApp(ctx, nil, opts...)
if err != nil {
log.Println("Error in initializing firebase", err)
return err
}
fcmClient, err := app.Messaging(ctx)
if err != nil {
log.Fatalf("error getting Messaging client: %v\n", err)
}
response, err := fcmClient.SendMulticast(ctx, &messaging.MulticastMessage{
Notification: &messaging.Notification{
Title: "Congratulations!!",
Body: "You have just implement push notification",
},
Tokens: deviceTokens,
})
if err != nil {
return err
}
log.Println("Response success count : ", response.SuccessCount)
log.Println("Response failure count : ", response.FailureCount)
return nil
}
func main() {
r := gin.Default()
deviceTokens, _ := db.RedisClient.SMembers(ctx,"fcmToken").Result()
SendPushNotification(deviceTokens)
r.Run()
}