A character has been replaced with another character. It's up to you to figure out which one it is. Explain why that character needs to be replaced with another one in order for this special sequence to be complete. They are arranged from the first to the last. Good luck.
-!--:!!!-- !!!--:-!- -!-:!!^- !!^-:!!!- !!!-:!- !-:!!^ !!^7:!!! ^---:!!