F5 APM One time Password as SMS using clickatell

In the "Variable Assign HTTP(1)" above I assume you do the same thing as described in the article, i.e. assigning the OTP and the "username" i.e. phone number to be used for the HTTP Auth? If so, the username assignment should at the moment look something like this:

session.logon.last.username = expr { [mcget {session.user.otp.mobile}]}

Change it to this:

session.logon.last.username = expr { "61[string range [mcget {session.user.otp.mobile}] 1 end]" }