I'm having trouble running my Expo project. When I run npx expo start or npx expo start --tunnel, the app doesn't load on my browser (http://localhost:8081/) or on my phone using the Expo Go app.

On the browser, I get:

"This page isn’t working right now. localhost didn’t send any data."

On my phone using Expo Go with the tunnel option, I get:

"There was a problem running the requested app. HTTP response error 503 ngrok gateway error nrr_ngrok_3004."

What I've tried:

• Using a different internet connection by enabling my mobile hotspot
• Disabling the firewall on my computer
• Creating a new Expo project using npx create-expo-app@latest and running it, but the issue persists

This project used to work fine before, but now nothing runs. Any ideas on how to fix this?

I'm having trouble running my Expo project. When I run npx expo start or npx expo start --tunnel, the app doesn't load on my browser (http://localhost:8081/) or on my phone using the Expo Go app.

On the browser, I get:

"This page isn’t working right now. localhost didn’t send any data."

On my phone using Expo Go with the tunnel option, I get:

"There was a problem running the requested app. HTTP response error 503 ngrok gateway error nrr_ngrok_3004."

What I've tried:

• Using a different internet connection by enabling my mobile hotspot
• Disabling the firewall on my computer
• Creating a new Expo project using npx create-expo-app@latest and running it, but the issue persists

This project used to work fine before, but now nothing runs. Any ideas on how to fix this?

• react-native
• expo
• ngrok

1 Answer 1

It turns out the issue was caused by an antivirus using port 8081. Before figuring this out, I tried running Expo on a different port with:

npx expo start --port 8082

And it worked, which indicated that port 8081 was blocked by another process.

To identify what was using port 8081, I followed these steps:

1. Check which processes are using port 8081 In the Command Prompt (cmd), I ran:

   netstat -ano | findstr :8081

The output was something like:

TCP 0.0.0.0:8081 0.0.0.0:0 LISTENING
4072

This means that the PID (Process ID) of the process using port 8081 was 4072.

2. Identify the program running on that PID Next, I ran:

   tasklist /FI "PID eq 4072"

This showed that the process running on port 8081 was macmnsvc.exe, which belongs to McAfee Antivirus.

3. Terminate the process to free the port Since I wanted to free up the port, I ran:

   taskkill /PID 4072 /F

This successfully killed the process, and after that, I was able to run Expo normally on port 8081 with:

npx expo start --tunnel