Oftentimes, the shipping address country is set to United States instead of Puerto Rico. This is because Puerto Rico is considered a US Territory. According to issue 97200, Fedex implementation requires Puerto Rico to be selected as country when shipping using "Fedex International Economy".
Below are the steps to correct the shipping address on the Item Fulfillment page.
1. On the Item Fulfillment page > click on Shipping Tab > Shipping Address section
2. On Country field, select Puerto Rico > Save
Note: UPS requires United States as country when shipping to Puerto Rico.