type cast of function arguments

I have written this little silly function

CREATE OR REPLACE FUNCTION recordMail(customerId_ integer, message_
VARCHAR(240)) RETURNS void AS $$
BEGIN
INSERT INTO MailRecord (custid,message) VALUES (customerId_, message_);
END;
$$ LANGUAGE plpgsql;

And it is created, and then I do:

select recordMail(10,'asd');

and I get

ERROR: function recordmail(integer, "unknown") does not exist
LINE 1: select recordMail(10,'asd');
^
HINT: No function matches the given name and argument types. You may
need to add explicit type casts.

What is wrong here and how do I fix it?