reply to you or reply you
I've learned I have to say "reply to someone" not "reply someone", but I found a following sentence;
Sorry for replying you so late.
Is this ok to say? Or ok when you text your friends?
Thank you!
This is wrong. You can either say:
Sorry for replying to you so late.
or
Sorry for replying so late.
You can never say 'reply me'. It's not a question of formality. It's wrong in any context.