I realize that hello is equivalent to hi, hey, what's up, etc. but technically they're not the same, so why is it marked wrong?
What's your question? The English word is hello so you need to translate it into a Swedish word. There are several options that are approved.
You probably left out "hallå," which is also correct.
I am writing "Hallå!" and is not accepted!!!!
I can see your error report as well. I have no idea why it isn't accepted - unfortunately, Duolingo sometimes bugs out, I'm guessing that's it. Restarting the lesson tends to help.
I thought that hello in swedish was Hallo not Halla with the little circle thing on top???
'Hallo' is german
How would i pronounce this? What effect does this 'å' accent have on the sound?
It's not an accent - å is its own letter! It's as different from a as d is from b.
You can find some good pronunciations here: https://forvo.com/word/hall%C3%A5/#sv