Yes, you would not have been allowed to board the plane without showing you paid the reciprocity. No problem now. And Uruguay does not have a visa fee for Americans.I am visiting in two weeks and I was under the assumption, after searching online, there was no charge for visa to enter Argentina and Uruguay. I don't have the links to where I found the information except I started with the US gov website back in December 2015. Either way this is good news and glad I wasn't surprised at airport. Do you know if there is a visa charge to enter Uruguay for US passport holder? I will be taking ferry. Thanks for all your posts!