1900: In The Struggle for Empire, by Robert William Cole, Iosia is a planet of an unnamed star somewhat more distant than Sirius:
For a long time past, a band of adventurers had been
colonizing a planet called Iosia, which was situated
far beyond the confines of the Sirian System.
The Struggle for Empire, Chapter III: The First Note of War
This planet is first colonized by Earth-humanity but coveted by the people of Kairet (a planet of Sirius) and becomes the flashpoint in the war.
After successfully defeating the Sirians, the Anglo-Saxon Empire (Earth) requires they also cede the planet Maikat:
The Anglo-Saxons demanded the evacuation of the planet that
had been the original cause of the war [Iosia], the surrender
of another planet called Maikat, that belonged to the Sirian
system, the payment of a huge war indemnity, and the limitation
of the Sirian war-ships for the future to their own planetary
ibid, Chapter XV: The End of the War