stackover flow link: error code :500 in react native

additional check would be checking sdk path, in android> local.properties, if not present create

//sdk.dir=/path/to/your/android/sdk
sdk.dir=/Users/<username>/Library/Android/sdk

replace your username in above line

Step 2: Set ANDROID_HOME Environment Variable

Aside from setting sdk.dir in local.properties, set the ANDROID_HOME environment variable in your system. Here's how you can do it on a Mac:

1. Open your terminal.

2. Run the following command to open the profile file in a text editor (it might be .bash_profile, .zshrc, or .bashrc depending on your system setup):

    nano ~/.zshrc
    # or
    nano ~/.bash_profile
   

3. Add the following line to the end of the file:

    export ANDROID_HOME=/Users/<username>/Library/Android/sdk
   

4. Save and exit (in nano, it's Ctrl+O to write changes and Ctrl+X to close the editor).

5. Load the new environment variables:

    source ~/.zshrc
    # or
    source ~/.bash_profile
   

6. Verify that the ANDROID_HOME variable is set correctly:

    echo $ANDROID_HOME
   

check if server is running, if that you can kill the process and rebuild

npx react-native start
//in other terminal tab
npx react-native run-android

if still doesn't work, try this

cd android && ./gradlew clean
cd .. && npx react-native run-android

npx react-native start --reset-cache

even after this you are not able to resolve the issue and getting this issue

address already in use :::8081. Error: listen EADDRINUSE: address already in use :::8081

then try kill the service running on port 8081

lsof -i :8081
kill -9 <PID>

npx react-native start