The mostly likely reason for getting that message is that the address you're entering is NOT one of the 48 contiguous U.S. States (these inside the red line).
We know it's frustrating, and we do apologize for the inconvenience. Unfortunately we have stopped shipping internationally due to the difficulty with many countries Customs holding, returning, or even disposing of product.
If you're trying to order accessories such as batteries, line, etc., it's possible there is something compatible that you can find locally, or online which you can order that you wouldn't have to pay international shipping for.
Just look for an 11.1V 1500mah 3-cell 25c LiPo battery that has an xt60 connector with a discharge rate that does not exceed 60c.