Subtitles added to mkv won't show up in jellyfin

[BigTomm]

I bought a copy of Godzilla Minus One in my recent visit to japan and I'm trying to add it to my jellyfin server with english subtitles. I was able to do so with an ASS file I found online and I added it successfully using mkvtoolnix. On my computer, the subtitles work great. But when I added Godzilla Minus One to my server it doesn't show the subtitles at all. It also pops up as "undefined" subtitles which didn't matter on my computer but it might on jellyfin? All help is greatly appreciated!