When i'm using this command
apex_application.g_print_success_message := '<span style="color:GREEN">Message</span>';
to show success message is works fine
but when i used the error command apex_application.g_print_error_message
it gives me this error, anyone can help-me
ORA-06550: line 10, column 20: PLS-00302: component 'G_PRINT_ERROR_MESSAGE' must be declared ORA-06550: line 10, column 3: PL/SQL: Statement ignored
apex_application.g_print_error_message
is a variable, so you can set it to a value like '<span style="color:GREEN">Message</span>' but you can't execute it as a "command".