Ok. I got it.
But it all feels so cumbersome, I better go with the recommended S3 bucket provider only, AWS !! So I again reinstated the Aws id and secret.
But in doing so, I faced a new hurdle. Even though I didn’t change even a small thing inside Aws interface, except making my login more stricter, now the media uploads done into it are visible in my website only if I turn on ‘Read’ access for all ‘Public’.
I don’t know how it was working earlier, and why only now I have to make my bucket contents ‘Permissions’ this way:
( Both showing in red color have been changed by me now, otherwise I’m not able to even preview my own uploads)