this seem to be the wrong character, you need to use ^ instead
also, you need to put it only right after the opening square parenthesis, if you put it other parts you are also including the character ^ in the character class
Worst case: just copy-paste the symbol here from a message ^^
Ofcourse if you work more with RegEx you need to figure out how to write the symbol. But if this single thing is blocking your learning progress, this is a way to work around it for the moment.