Bills a single customer now, in the same fashion as the "Bill now" link in the
UI.
-Returns a hash reference with a single key, 'error'. If there is an error,
-the value contains the error, otherwise it is empty.
+Returns a hash reference with a single key, 'error'. If there is an error,
+the value contains the error, otherwise it is empty. Takes a list of keys and
+values as parameters with the following keys:
+
+=over 4
+
+=item secret
+
+API Secret (required)
+
+=item custnum
+
+Customer number (required)
+
+=back
=cut