htmlspecialchar(), htmlentities(), or mysqli_real_escape_string() is my issue somewhere is my code.

<?php 
include '../../core/init.php'; 
members_only();
include '../../includes/overall/header.php'; 

if(isset($_POST["post_type"])) {
    $post_type = $_POST['post_type'];
    $post_body = $_POST['post_body'];
    $post_body = nl2br(htmlentities($post_body));
    $forum_section_id = (int)$_POST['fsID'];
    $forum_section_title = htmlentities($_POST['fsTitle']);
    $member_id = (int)$_POST['uid'];
    $post_author = $_POST['username'];
    $post_title = preg_replace('#[^A-Za-z0-9 ?!.,]#i', '',$_POST['post_title']);

    if ($post_type == "a") {
        if ($post_title == "") {
            echo 'Your Title is missing';
        }
        if (strlen($post_title) < 10) {
            echo 'The Title needs to be at least 10 characters';
        }
        if (strlen($post_body) < 2) {
            echo 'Your body needs to be at lease 2 characters';
        }
        $sql = "INSERT INTO forum_post (post_author, post_author_id, date_time, type, section_title, section_id, thread_title, post_body) VALUES ('$post_author', '$member_id', CURRENT_TIMESTAMP, 'a', '$forum_section_title', '$forum_section_id', '$post_title', '$post_body')";
        $query = mysqli_query($mysqli, $sql) or die(mysqli_error($mysqli));
        $this_id = mysqli_insert_id($mysqli);
        $sql = "UPDATE forum_post SET otid = '$this_id' WHERE id = '$this_id'";
        $query = mysqli_query($mysqli, $sql) or die(mysqli_error($mysqli));
        echo "post_success";
        exit();
    }
}
if (isset($_GET['id']) && isset($_GET['title'])) {
    $section_id = $_GET['id'];
    $section_title = $_GET['title'];
} else {
    header('Location: message.php?msg=Stop messing with the urls');
}
?>

<?php 
include '../../core/init.php'; 
members_only();
include '../../includes/overall/header.php'; 

$myAgoObject = new convertToAgo;

//Get the Id from the URL
$thread_id = (int)$_GET['id'];

//Checking to make sure the thread id exists
$query = mysqli_query($mysqli, "SELECT * FROM forum_post WHERE id = '$thread_id' AND type = 'a' LIMIT 1");
$numRows = mysqli_num_rows($query);

if ($numRows < 1) {
    $errors[] = 'That Thread does not exist. Stop playing with the URL\'s';
    exit();
} else {
    $sql = "UPDATE forum_post SET view_count = view_count + 1 WHERE id = $thread_id";
    $upcount = mysqli_query($mysqli, $sql);
}

//Setting all varibles
while ($row = mysqli_fetch_array($query)) {
    $post_author = $row['post_author'];
    $post_author_id = $row['post_author_id'];
    $date_time = $row['date_time'];
    $date_time = strftime('%b %d, %Y', strtotime($date_time));
    $section_title = $row['section_title'];
    $section_id = $row['section_id'];
    $thread_title = $row['thread_title'];
    $post_body = mysqli_real_escape_string($mysqli, $row['post_body']);
}

// now query an responses out of the database
$all_responses = '';
$query = mysqli_query($mysqli, "SELECT * FROM `forum_post` WHERE `otid` = '$thread_id' AND `type` = 'b'");
$numRows = mysqli_num_rows($query);
if($numRows < 1) {
    $all_responses = '<div class="alert alert-info text-center" role="alert">No one has respond to this post! You can be the first to post.<br></div>';
}else {
    while ($row = mysqli_fetch_array($query)) {
        $reply_author = $row['post_author'];
        $reply_author_id = $row['post_author_id'];
        $date_n_time = $row['date_time'];
        $converted_time = ($myAgoObject -> convert_datetime($date_n_time));
        $whenReply = ($myAgoObject -> makeAgo($converted_time));
        $reply_body = mysqli_real_escape_string($mysqli, $row['post_body']);
        $avaquery = mysqli_query($mysqli, "SELECT * FROM users WHERE username = '$reply_author' AND activated = '1'");
        $userRow = mysqli_fetch_array($avaquery);
        $userLevel = $userRow["userlevel"];
        $signup = $userRow["signup"];
        $signup = strftime("%b %d, %Y", strtotime($signup));
        $lastLogin = $userRow["lastlogin"];
        $lastLogin = strftime("%b %d, %Y", strtotime($lastLogin));
        $avatar = $userRow["avatar"];
        $country = $userRow["country"];
        $post_author_avatar = '<img src="/user/' . $reply_author . '/' . $avatar . '" alt="' . $reply_author . '" class="user_pic">';
        if($avatar == NULL){
            $post_author_avatar = '<img src="/img/avatardefault.gif" alt="' . $reply_author . '" class="user_pic">';
        }
        $all_responses .= '<tr>';
        $all_responses .=   '<td class="td-user">';
        $all_responses .=       '<div class="forum-user-info">';
        $all_responses .=           '<a href="/' . $reply_author . '">' . $reply_author . '</a><br>' . $post_author_avatar . '<br>';
        $all_responses .=           'Access: ' . $userLevel . '<br>';
        $all_responses .=           'Joined: ' . $signup . '<br>';
        $all_responses .=           'Last Logged: ' . $lastLogin . '<br>';
        $all_responses .=       '</div>';
        $all_responses .=   '</td>';
        $all_responses .=   '<td class="td-reply">';
        $all_responses .=       '<div class="forum-reply">';
        $all_responses .=           $reply_body;
        $all_responses .=       '</div>';
        $all_responses .=       '<div class="forum-posted">';
        $all_responses .=           'Posted: ' . $whenReply;
        $all_responses .=       '</div>';
        $all_responses .=       '<div class="forum-reply-control clearfix">';
        $all_responses .=           'Like &bull; &nbsp;';
        $all_responses .=           'Edit &bull; &nbsp;';
        $all_responses .=           'Delete';
        $all_responses .=       '</div>';
        $all_responses .=   '</td>';
        $all_responses .= '</tr>';
    }
}

$editPostbtn = '<button class="btn btn-primary btn-lg" data-toggle="modal" data-target="#editPost">Edit</button>';
?>