Hello,
define your filter expression like following:
in("CARRID", $$P_CARRID$$)
=> the parameter must not be enclosed in quotes
Regarding the input:
Your second option is correct. For every value an own line has to be entered with a single value.
If you do not get a result then, please check your view settings (e.g. you have set session client as default client, you will not get a result if no session client is set for your user).
Best Regards,
Florian