Serving SPA with Golang and Chi router enters a loop

I´m trying to serve a SPA with Golang and solving the 404 error became a challenge.

• In the init() func I buffered into memory the index.html file.
• I created a indexHandler that returns the index file buffered.
• I call the indexHandler in the router.NotFound() func so the route is returned to the SPA.
• I serve the rest of the static files with FileServer.

The problem is that it seems to be in a loop, when I try to access the app in the browser, it reloads itself indefinitely.

package main

import (
    "log"
    "net/http"
    "os"
    "path/filepath"
    "time"

    "github.com/go-chi/chi/v5"
    "github.com/go-chi/chi/v5/middleware"

    "github.com/joho/godotenv"
)

var indexBuffer []byte

func main() {   
    r := chi.NewRouter()
    
    r.Use(middleware.RequestID)
    r.Use(middleware.RealIP)
    r.Use(middleware.Logger)
    r.Use(middleware.Recoverer)

    fs := http.FileServer(http.Dir(os.Getenv("FRONTEND_PATH")))
    r.Handle("/app/static/*", http.StripPrefix("/app/static/", fs))

    apiRouter := chi.NewRouter()
    apiRouter.Get("/cargas", handlerCargas)

    r.Mount("/app/api", apiRouter)

    r.NotFound(indexHandler)

    log.Fatal(http.ListenAndServe(":8000", r))
}

func init() {
    err := godotenv.Load()
    if err != nil {
        log.Fatal("Erro ao ler .env verifique!")
    }

    indexBuffer, err = os.ReadFile(filepath.Join(os.Getenv("FRONTEND_PATH"), "index.html"))
    if err != nil {
        log.Fatal("Erro ao tentar bufferizar a index na init().")
    }
}

func indexHandler(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "text/html")
    w.Write(indexBuffer)
}

I´m expecting index.html to be served by the indexHandler and the rest of the files be served by the FileServer and errors of page not found be handled by the SPA.