His Majesty the Emperor of all the Russias agrees to cede to the United States, by this convention, immediately upon the exchange of the ratifications thereof, all the territory and dominion now possessed by his said Majesty on the continent of America
to cede is not to sell.

In the Russianversion of the treaty it is "уступать".

Если взять толковый словарь того времени, то "уступать" значит: "давать на время, давать в аренду", но не "продавать".