There are a couple slightly different ways to say goodbye, depending on if you’re the person staying (and the other person is leaving) or you’re the person leaving (and the other person is staying).

If you’re the person leaving, it’s 안녕히 게세요
If you’re the person staying, you can say 안녕히 가세요 (you can also say 잘가(요) – “Go well.”)

However, that can all be a bit confusing and hinder your fluency when trying to speak so I’m going to give you a tip – the exact way I do it. I NEVER differentiate between hello (안녕하세요) or goodbye. Say them quick enough (almost slurring it all together) and they all sound basically the same. I’ve been using this technique in Korea for 6 years now and it is always fine, and actually, the day I started doing it, I started getting compliments on how well I spoke (even though I’d only said “Hello”). Hope that helps!

You’re very right about that. Originally I just made that in
response to a question from another site, but yeah, I should
definitely get on making a video for that.

Thanks!