Way 1 · best default
Sorry for the late reply
The standard opener. One short line, then answer the message.
Examples
Sorry for the late reply! Yes, Saturday works for me.
Hi Tom, sorry for the late reply. I've attached the file.
In a conversation
A: Did you get my message about the trip?
B: Yes, sorry for the late reply. I'm in!
Common mistake
Not: Sorry for replying you late.
Say: Sorry for the late reply.
"Reply you" is wrong (it's "reply to you"), and "the late reply" sounds more natural anyway.
