Error "Service not found" when trying to authenticate user using auth0 in React app with Express.js backend


I’m currently working on a React application with an Express.js backend where I’m trying to authenticate users using the Auth0 package. I have a setup where the frontend and backend communicate through API requests.

In my React app, I’m encountering an error: “Service not found: http://localhost:5000” when trying to make a request from the frontend to the backend after obtaining an access token. I’ve checked the configurations and URLs, but I can’t seem to pinpoint the issue.

Here’s the relevant code:

Frontend: I’m using the useMutation hook to make the API request after obtaining the access token.

const { mutate } = useMutation({
  mutationKey: [user?.email],
  mutationFn: async (token) => {
    try {
          email: user?.email,
          headers: {
            Authorization: `Bearer ${token}`,
    } catch (error) {
      console.error("An error occurred:", error);
      throw error;

Backend: I’m using the express-oauth2-jwt-bearer package to perform JWT token validation.

import { auth } from "express-oauth2-jwt-bearer";

export const jwtCheck = auth({
  audience: "http://localhost:5000",
  issuerBaseURL: "",
  tokenSigningAlg: "RS256",

I’ve verified that the URLs, CORS configuration, and token audience match on both the frontend and backend. The Express.js server is running on http://localhost:5000.

What could be causing this “Service not found” error? Are there any common pitfalls or misconfigurations I should be aware of when setting up this type of authentication flow between a React app and an Express.js backend?

Any help or insights would be greatly appreciated. Thank you!

1 Like

Hi @santhoshprabhakaran0,

Welcome to the Auth0 Community!

Thanks for the thorough question.

The service not found error indicates that the service for which you are requesting a token (http://localhost:5000) hasn’t been registered with Auth0. Have you set up an API in the Auth0 dashboard and set the correct identifier?

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