Steps:
1. Go to Home Page
2. Scroll Down
3. Click Donate Button
4. Go to Private Donations
5. Select Pay Each Month
6. Fill out the Postal Code/Zip Code
7. Observe 

Actual: Verify the Postal Code/Zip Code by entering Special Characters and Letters Value	

Expected: Should not able entering Special Characters and Letters in text box

Screenshot: https://screencast-o-matic.com/watch/c3fhexVqxcv