Authorization fuzz

[JackandBlackLLL]

Sorry for posting here, but I don't know where else to ask this question.
I'm trying to brute-force basic authentication.
She looks like
Authorization: Basic Z3NlZ3NlOmdzZWdlcw==

That is, I have to take the login and password and convert to base64.
wfuzz -z file,usernames.txt -z file,passwords.txt --zE base64 --basic FUZZ:FUZ2Z https://www.site.com/authentication
But it doesn't work, wfuzz just won't run (without any errors).
How should I use encoder to get the payload gsegse:gseges first, then convert that to base64 ?