By default, Title and Message maximum text length seems to be unlimited. I tried Title and Message text length more 1,000 characters and message successfully sent.

I added the following code in functions.php in child theme.

add_filter( 'fep_form_fields', function( $fields ) {
    $fields['message_title']['maxlength'] = 50;
    $fields['message_content']['maxlength'] = 200;
    return $fields;
});

I tried Title and Message text length more 1,000 characters and message successfully sent.

Please advise how to set Title and Message maximum text length.

Thanks.