Heroku application error when deploy go fiber app - go

Question

When I deploy my go fiber app to heroku, I got the following error
2022-08-23T15:33:03.334087+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/swagger/index.html" host=vast-ocean-37337.herokuapp.com request_id=9161bdfc-ff62-4b5e-bd99-1649f7f5e569 fwd="173.32.236.24" dyno= connect= service= status=503 bytes= protocol=https
and this is my main.go file
package main
import (
"os"
"github.com/gofiber/fiber/v2"
"github.com/gofiber/fiber/v2/middleware/cors"
"github.com/gofiber/fiber/v2/middleware/recover"
"rocketstothemoon.com/configs"
"rocketstothemoon.com/routes"
fiber_swagger "github.com/swaggo/fiber-swagger"
_ "rocketstothemoon.com/docs"
)
func main() {
app := fiber.New()
app.Use(recover.New())
app.Use(cors.New())
configs.ConnectDB()
routes.UserRoute(app)
app.Get("/swagger/*", fiber_swagger.WrapHandler)
serveStatic(app)
port := os.Getenv("PORT")
if port == "" {
port = "3000"
}
app.Listen(":" + port)
}
func serveStatic(app *fiber.App) {
app.Static("/", "./build")
}
It works perfectly fine in my local, but keep throwing this error in heroku.
I have changed my port to os.Getenv("PORT") but it doesn't help, any help?