Electron: Send message from React to Main

I am trying to send information from my react code (through ipcRenderer) to my index.electron.js file (listening on ipcMain), but the message is not being picked up.

The exact flow is:

1. Send message from mainWindow.webContents
2. Execute some react code
3. Send message from react code back to electron
4. Electron listens to the message and executes a zoomFactor change

My code is as follows:

index.electron.js:

const ipcMain = require('electron').ipcMain;

...

click: () => mainWindow.webContents.send('TEST-1', 'message sent from mainWindow') // this works

...

ipcMain.on('TEST-2', (event, arg) => { // this does not work
    console.log('IPC MAIN', arg);
});

some-react-component.js

ipcRenderer.on('TEST-1', (event, message) => { // this works
    console.log('react-component', message);
    ipcRenderer.send('TEST-2', 'message sent from react');
});
ipcRenderer.on('TEST-2', (event, message) => { // this works (this is just to check if TEST-2 is sending
    console.log('react-component', message);
});

The ipcRenderer is picking up the message sent on channels TEST-1 and TEST-2, but I cannot get the ipcMain to listen on TEST-2

Thanks :)