Help with e visa

Hi, am planning on applying for e visa using my Irish passport. I also have British passport and am a little confused about what to put on form where it asked if you have or did have another nationality ?

Why you dont just list your British citizenship and that’s it?

i don’t understand the issue.

Because it’s easier (and cheaper) for me to use Irish passport.

You can only obtain an e visa using your Irish Passport any way, UK passport holders are unable to apply for a Russian e visa