What is the best method to display error messages from a database stored procedure called from a dynamic action ? By default I get a very unfriendly message.

I have tried the following in the exception section of my database stored package, but only the popup above appears , rather than the user friendly in-line error
exception
when app\_error
then
apex\_error.add\_error
(
p\_message => msg\_op,
p\_display\_location => apex\_error.c\_inline\_in\_notification
);
raise;
when others
then
msg\_op := 'Unhandled Error at Error Point: '
|| err\_point\_lv
|| ' SQL ERROR '
|| ' \[ '
|| sqlerrm
|| ' \].'
|| ' PROCEDURE : '
|| proc\_nm\_lv
|| '. Process Terminated....';
apex\_error.add\_error
(
p\_message => msg\_op,
p\_display\_location => apex\_error.c\_inline\_in\_notification
);
raise;