Hi! Thanks for reaching out. I want to help you with the issue you're having in the USPS app where you can’t switch from letters to numbers while entering your email address. Just to clarify a bit:

1. Are you trying to enter numbers in the email address field (which normally doesn’t require numbers, but can include them)?
2. Or is the keyboard input itself stuck on letters only and you can’t switch to the number keyboard on your Mac?
3. Are you using the USPS app on a Mac (since you mentioned OS X 10.15.7), or is this in a web browser?

This info will help me provide precise instructions for your issue. Meanwhile, here are some things to try based on common issues with keyboard input switching on macOS:

### Basic Troubleshooting Steps:
1. Check Keyboard Input Source:
- Click the input language or keyboard icon on the top right menu bar (near the clock).
- Make sure the proper keyboard language or input source is selected.
- Try toggling to a different keyboard and back.

2. Try Using Keyboard Shortcut to Switch Input:
- On Mac, press Control + Shift + Space or Command + Space to cycle through input sources.

3. Restart the App or Browser:
- If the problem is with the USPS app, quit it completely and relaunch.
- If you’re using a browser, close the tab or browser window and re-open the USPS site.

4. Reboot Your Mac:
- Sometimes a restart smooths out input glitches.

If the issue is with the app itself not allowing you to enter numbers specifically in the email field, it might be a bug or a limitation. In that case:

- Check if there is an update to the USPS app on the App Store and install it.
- Clearing the app cache or reinstalling can help if the app is stuck.
- Alternatively, try entering your email address using a browser instead of the app.

Let me know exactly what you’re seeing and trying so I can guide you next! Are you able to switch keyboards on your Mac normally outside the USPS app?

The app won't allow me to go from letters to numbers as to enter my email address