What will be the procedure to run a job scheduler to send mails on apex oracle?

I have an apex application where i need to send a notification mail to all the employees on the 5th of every month. So just for the sake of testing i am trying to send a mail in every 30 seconds. I created a job scheduler on a procedure to do the same. Here is the PLSQL code for it.

create or replace procedure send_notification_employee as
cursor c_employee is select * from EMPLOYEE;
r_employee c_employee%ROWTYPE;
begin
    open c_employee;
    loop
        fetch c_employee into r_employee;
        exit when c_employee%NOTFOUND;
        APEX_MAIL.SEND(
        p_to        => r_employee.EMPLOYEE_EMAIL,
        p_from      => 'abc@gmail.com',
        p_subj      => 'Reminder : Meeting',
        p_body      => '<Some random message>');
    end loop;
    close c_employee;
end;
/

begin    
DBMS_SCHEDULER.CREATE_JOB(
    job_name => 'send_notification',
    job_type => 'stored_procedure',
    job_action => 'send_notification_employee',
    start_date => NULL,
    repeat_interval => 'FREQ=SECONDLY;INTERVAL=30',
    end_date => NULL);
end;
/

begin
DBMS_SCHEDULER.enable(
    name => 'send_notification');
end;
/

I guess the code is correct. The only thing i am not sure of is to how to run this scheduler on the apex oracle application. Should i just execute these statements on the SQL Commands or is there any other way to do it?

Also i tried to execute the same statements in the SQL Commands tab but i don't receive any mails as such. Is there any issue with my code? Thanks in advance.

You need to set the security group if sending the mail from the database rather than from APEX directly. You should also use push_queue at the end of the procedure to clear out the table of unsent mail.

create or replace procedure send_notification_employee as
cursor c_employee is select * from EMPLOYEE;
r_employee c_employee%ROWTYPE;
l_workspace number;
begin
    -- Get the workspace ID
    l_workspace := apex_util.find_security_group_id(<workspace name>);

    -- Set Workspace
    apex_util.set_security_group_id(l_workspace);

    open c_employee;
    loop
        fetch c_employee into r_employee;
        exit when c_employee%NOTFOUND;
        
        APEX_MAIL.SEND(
        p_to        => r_employee.EMPLOYEE_EMAIL,
        p_from      => 'abc@gmail.com',
        p_subj      => 'Reminder : Meeting',
        p_body      => '<Some random message>');
    end loop;
    close c_employee;
    
    -- Finally force send
    APEX_MAIL.PUSH_QUEUE;
end;

Re. how to execute - it depends on what you want to do. If you just want to run it on the 5th of every month just setup a scheduled job in the db to do it, as you have above. If you want to run on an adhoc basis just create a job in an APEX after submit process that calls the procedure and executes through the database.

As an aside, if you plan to create many mail procedures you may wish to create a helper procedure to get the workspace id / send the mail, and just call it from your other mail procedures.