$json = json_decode($result, true);
foreach( $json as $key => $value ) {
    if( $key == "purchase" ) {
        $purchase = json_decode( $value,true );
        foreach( $purchase as $subkey => $subvalue ) {
            if( $subkey == "email" ) {
                if( $subvalue == $email ) {
                    echo "\n\nVALID EMAIL\n\n";
                                    break;
                                } else {
                                    echo "\n\n\n ******* NON-VALID EMAIL ******* \n\n\n";
                                }
                        }
        }
        break;
    }
}