what does the error mean?

The username which you entered is not exist. please try to use another username.

username is the which we use to login into the environment?

then use user(loggedInUser(),"firstName")&" "&user(loggedInUser(),"lastName")

i wanted to when i can set a rule input of user type?

this is fine i understood

because in an expression rule the rule input can be of primitive data types, CDT and record types right?

if the username which you are sending is valid then you can use the code below.

can you show me the rule input part?

it is there in the snapshot i attached

userName is of type text right?

from the outside you can use like rule!{your expression rule name}(your input variable) forexample: rule!getDisplayName("dgupta")

from the outside you can use like rule!{your expression rule name}(your input variable) forexample: rule!getDisplayName("dgupta")

okay thanks