apparently some people end up not having a checksumfile to begin with in their gog version.
https://windowsforum.com/threads/how-to-get-stellaris-gog-vs-steam-working-in-multiplay.241690/
Just email your friend the checksum file and their gog version can play with you.
https://windowsforum.com/threads/how-to-get-stellaris-gog-vs-steam-working-in-multiplay.241690/
Just email your friend the checksum file and their gog version can play with you.