web_set_user with parameters

I need your help here with this function.

When I hardcode the arguments, like:

web_set_user ("John", "thisismypassword", "yyy.com:80")

The script runs fine and executes all the transactions. No problem at all.

But, when I try to use a parameter for the argument user, LR gives me an error:  401 for Unauthorized...

I tried:

web_set_user ("{User}", "thisismypassword", "xxx.com:80")

I exposed to the console the content of the parameter user and it looks fine: John

I really don't know what's going on.

What's the correct syntax for this function in order to use it with parameters?