Paying for proton with cash

> If you’re just sending correspondence (no trading cards, bookmarks, stickers, etc.) or nonnegotiable documents (just paper; no cash, checks, or other items that have cash value), you don’t need a customs form. The Step 1 on How To Send A Letter or Postcard: International | USPS has that no cash part. I’ll do what you guys did since it worked. I guess I’ll know what happened in like 6 weeks .