I recently contacted a representative concerning the standard envelope shipping option not showing up as an option. I figured it out myself, seems their default dimensions are 12X7X1. I changed the dimensions to a #10 envelope which is 10X5X0.2 inches and that worked. It would be senseless to sell an item for $3.99 and pay that much or more to ship USPS first class. Just a heads up for everyone who sells coins/tokens/trading cards.
