I saw a answer, but even though it was correctly pointing OP's mistake, the answer read as the poster was trying to get some clarification from the OP; and the answer was too short. The answer got downvoted.
Are you using in-memory or database authentication? I don't see any. Refer this link for step by step guide.
I would modify it as follows:
In your configuration you are missing authentication part that is why your authentication is getting failed.
You can use configure authentication by auth-config1
bla bla bla
You can use configure authentication by auth-config2
bla bla bla
For step by step guide refer this link
I don't see anything great for writing my own answer instead of editing the correct answer.
Now my question: if that answer gets accepted or gets upvotes in future (after getting edited), is there any badge rewarding the person who edited it?
No, there's no such a badge. Editing posts will count towards the Struck and White/Copy Editor badges, though.
But there was a hat in 2018's Winter Bash that had such a trigger:
Edit 5 questions that later get upvoted.
Trigger confirmed by Catija here.