This is due to Sony, not MSE or Raiders.
It's because you and your friend are in different regions, such as NA vs. EU, and Sony has different PSN stores per region, and thus even the same game bought on 2 different PSN regions will be a different "product".
So MSE cannot fix this. Though I hear that the upcoming Guild update will allow cross platform invitations, which would also fix this PS4 issue of cross-region trouble.
Other users have found a work around to be if you create a new dummy PSN account in a different region and download a second version of Spacelords, you can then go back to your main account and invites will work, because you will have the files for both regions on your PS4.