Very simply, the -g option is not recognized as a valid option for the typeset command in the shell you're using; so it gives you an error.

What does the man page for the shell that was used to interpret the script that was successfully using typeset -g say the -g option is supposed to do?

Are you using the same shell on the same system where typeset -g was used by the other user? What shell are you using? What OS are you using?

Why is it important for you to copy someone else's code if you don't know what it is trying to do?