I read a post about someone with a similar problem as mine, but his answer didn't seem to work for me!

I had the USPS module reinstalled after I updated zen-cart to 1.3.8, and figured out how to change the shipping weight to 0:0 to get first class to show up on domestic, but it still doesn't show up for international, although I've checked on USPS.COM and they do offer 1st class international for all the countries I tested.

I would like to offer this to my customers. Any idea on what is happening?
Thanks!