declare x number;
begin
x := db_mail.send_mail ('falkson@etisales.com', 'New great product in our store',

'We are happy to offer the product that you have asked for. For details please see the attached picture.',

'falkson@etisales.com', 1, 'text/html' ) ;
---dbms_output.put_line(x);
---EXCEPTION WHEN OTHERS THEN NULL;
end;

GETTING

ORA-06502: PL/SQL: numeric or value error: character to number conversion error

You last 2 parameters in the wrong order, email type goes first then goes priority.

: declare x number;
: begin
: x := db_mail.send_mail ('falkson@etisales.com', 'New great product in our
: store',

: 'We are happy to offer the product that you have asked for. For details
: please see the attached picture.',

: 'falkson@etisales.com', 1, 'text/html' ) ;
: ---dbms_output.put_line(x);
: ---EXCEPTION WHEN OTHERS THEN NULL;
: end;

: GETTING

: ORA-06502: PL/SQL: numeric or value error: character to number conversion
: error