assistance file update

I need to update the query Substract from todays date the date on my DB in order to show the customers that are with their payments up to date I can send file or share github address [login to view URL] //original query $query = mysqli_query($mysqli,"SELECT * FROM registrados WHERE actividad = " . $fetch_actividad['id_actividad'] . " ORDER BY apellido ASC"); // $query = mysqli_query($mysqli,"SELECT * FROM registrados WHERE actividad = " . $fetch_actividad['id_actividad'] . AND "mes_pagado between now() - interval 40 day" . " ORDER BY apellido ASC"); //$query = mysqli_query($mysqli,"SELECT * FROM registrados WHERE actividad = " . $fetch_actividad['id_actividad'] . AND CURDATE()-registrados.mes_pagado< DATE_SUB("mes_pagado", INTERVAL 40 DAY) . " ORDER BY apellido ASC");