Problems inserting into database after server upgraded PHP and SQL - .htaccess

Question

If I don't explain this issue properly, please say and I'll edit it to suit.
I have a program called 'LiveAgent' which relies heavily on SQL insertion and retrieval - which was working untl my server upgraded the PHP from 7.0 to 7.2, and the SQL from 10.1 to 10.2.17_MariaDB. I've been told the .htaccess needs changing so the software can communicate with the server. I'm very confused. The software shows all entries until the 22nd, when the server was upgraded (UK2). Since then you can't submit anything into it.
The htaccess file is below. As is the code for adding an 'appointment'.
HTACCESS
# Mod Rewrite
Options +FollowSymLinks
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
RewriteCond %{HTTPS} !on
RewriteCond %{REQUEST_URI} !^/[0-9]+\..+\.cpaneldcv$
RewriteCond %{REQUEST_URI} !^/\.well-known/pki-validation/[A-F0-9]{32}\.txt(?:\ Comodo\ DCV)?$
RewriteRule (.*) https://%{HTTP_HOST}%{REQUEST_URI}
#Fix Rewrite
Options -Multiviews
#http://forum.codecall.net/topic/74170-clean-urls-with-php/
<IfModule mod_deflate.c>
# Compress HTML, CSS, JavaScript, Text, XML and fonts
AddOutputFilterByType DEFLATE application/javascript
AddOutputFilterByType DEFLATE application/rss+xml
AddOutputFilterByType DEFLATE application/vnd.ms-fontobject
AddOutputFilterByType DEFLATE application/x-font
AddOutputFilterByType DEFLATE application/x-font-opentype
AddOutputFilterByType DEFLATE application/x-font-otf
AddOutputFilterByType DEFLATE application/x-font-truetype
AddOutputFilterByType DEFLATE application/x-font-ttf
AddOutputFilterByType DEFLATE application/x-javascript
AddOutputFilterByType DEFLATE application/xhtml+xml
AddOutputFilterByType DEFLATE application/xml
AddOutputFilterByType DEFLATE font/opentype
AddOutputFilterByType DEFLATE font/otf
AddOutputFilterByType DEFLATE font/ttf
AddOutputFilterByType DEFLATE image/svg+xml
AddOutputFilterByType DEFLATE image/x-icon
AddOutputFilterByType DEFLATE text/css
AddOutputFilterByType DEFLATE text/html
AddOutputFilterByType DEFLATE text/javascript
AddOutputFilterByType DEFLATE text/plain
AddOutputFilterByType DEFLATE text/xml
# Remove browser bugs (only needed for really old browsers)
BrowserMatch ^Mozilla/4 gzip-only-text/html
BrowserMatch ^Mozilla/4\.0[678] no-gzip
BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
Header append Vary User-Agent
</IfModule>
## EXPIRES CACHING ##
<IfModule mod_expires.c>
ExpiresActive On
ExpiresByType image/jpg "access plus 1 year"
ExpiresByType image/jpeg "access plus 1 year"
ExpiresByType image/gif "access plus 1 year"
ExpiresByType image/png "access plus 1 year"
ExpiresByType text/css "access plus 1 month"
ExpiresByType application/pdf "access plus 1 month"
ExpiresByType text/x-javascript "access plus 1 month"
ExpiresByType application/x-shockwave-flash "access plus 1 month"
ExpiresByType image/x-icon "access plus 1 year"
ExpiresDefault "access plus 2 days"
</IfModule>
## EXPIRES CACHING
# php -- BEGIN cPanel-generated handler, do not edit
# Set the “ea-php70” package as the default “PHP” programming language.
<IfModule mime_module>
AddType application/x-httpd-ea-php70 .php .php7 .phtml
</IfModule>
# php -- END cPanel-generated handler, do not edit
AJAX:
if($ajax['1'] == 'add_new_appointment'){
include 'files/add_new_appointment.php';
}
ADD NEW APPOINTMENT
<form action="" method="post" class="form-horizontal" >
<div class="modal-body">
<?php // ------------- ERROR -----------------
foreach ($notification_msg as &$notification) { ?>
<div class="alert <?php echo $notification['type'] ?>"><button type="button" class="close" data-dismiss="alert">×</button><strong><?php echo $notification['h4'] ?> </strong> <?php echo $notification['msg'] ?></div>
<?php } // ------------- ERROR ----------------- ?>
<input type="hidden" name="session_id" value="<?php echo $ajax['0'] ?>">
<input type="hidden" name="create_appointment" value="true">
<div class="form-group">
<label class="col-sm-3 control-label">Find Customer *</label>
<div class="col-sm-9">
<select name="customer" id="customer-single" style="width:100%" required>
<option value="">Select a customer</option>
<?php foreach(customer_array($ajax['0']) as $customer){ ?>
<option value="<?php echo $customer['id'] ?>"><?php echo $customer['business_name'] ?> - <?php echo $customer['first_name'] ?> <?php echo $customer['last_name'] ?></option>
<?php } ?>
</select>
If your customer is not listed you can add them here.
</div>
</div>
<hr>
<div class="form-group">
<label class="col-sm-2 control-label">Category *</label>
<div class="col-sm-10">
<select name="category" id="category-single" style="width:100%" required>
<option value="">Select a category</option>
<?php foreach(category_array($ajax['0']) as $category){ ?>
<option value="<?php echo $category['id'] ?>"><?php echo $category['name'] ?></option>
<?php } ?>
</select>
</div>
</div>
<div class="form-group">
<label class="col-sm-2 control-label">Date *</label>
<div class="col-sm-4">
<input class="form-control datepicker" type="text" name="date" required>
</div>
<div class="col-sm-1">
<label class="control-label">Time *</label>
</div>
<div class="col-sm-2">
<input class="form-control timepicker" type="text" name="start_time" required>
</div>
<div class="col-sm-1">
<label class="control-label">To *</label>
</div>
<div class="col-sm-2">
<input class="form-control timepicker" type="text" name="end_time" required>
</div>
</div>
<div class="form-group">
<label class="col-sm-3 control-label">Booked By *</label>
<div class="col-sm-9">
<select name="booked_by" id="agent-single" style="width:100%" required>
<?php foreach (agent_array($ajax['0']) as $agent){ ?>
<option <?php if($agent['id'] == get_agent_from_session($ajax['0'], 'id')){echo 'selected';} ?> value="<?php echo $agent['id'] ?>"><?php echo $agent['first_name'] ?></option>
<?php } ?>
</select>
</div>
</div>
<div class="form-group">
<label class="col-sm-3 control-label">Booked for *</label>
<div class="col-sm-9">
<select name="booked_for[]" id="agent-multi" multiple="multiple" style="width:100%" required>
<?php foreach (agent_array($ajax['0']) as $agent){ ?>
<option value="<?php echo $agent['id'] ?>"><?php echo $agent['first_name'] ?></option>
<?php } ?>
</select>
</div>
</div>
<div class="form-group">
<label class="col-sm-2 control-label">Notes</label>
<div class="col-sm-10">
<textarea class="form-control" name="notes"> </textarea>
</div>
</div>
</div>
<div class="modal-footer">
Close
<button type="submit" class="btn btn-success">Save</button>
</div>
</form>
DATABASE CONNECTION
// arrays
$notification_msg = array();
$bank_holidays = array();
// connect to db
try {
$dbh = new PDO("mysql:host=$dbhostname;dbname=db", $dbusername, $dbpassword);
/*** echo a message saying we have connected ***/
//$notification_msg[] = array(type=>'alert-success', h4=>'Success', msg=>'Connected to database');
}
catch(PDOException $e)
{
$notification_msg[] = array(type=>'alert-success', h4=>'', msg=>$e->getMessage());
}
PHP/SQL Code:
if($_POST['create_appointment']){
$customer_id = htmlspecialchars($_POST['customer'], ENT_QUOTES);
$category_id = htmlspecialchars($_POST['category'], ENT_QUOTES);
$date = htmlspecialchars($_POST['date'], ENT_QUOTES);
$start_time = htmlspecialchars($_POST['start_time'], ENT_QUOTES);
$end_time = htmlspecialchars($_POST['end_time'], ENT_QUOTES);
$booked_by = htmlspecialchars($_POST['booked_by'], ENT_QUOTES);
$booked_for = post_array_to_explode($_POST['booked_for']);
$notes = htmlspecialchars($_POST['notes'], ENT_QUOTES);
$session_id = htmlspecialchars($_POST['session_id'], ENT_QUOTES);
$time = date("Y-m-d H:i:s");
$agent_id = get_agent_from_session($session_id, 'id');
$start_date = $date.' '.$start_time;
$end_date = $date.' '.$end_time;
$start_date = format_datetime_mysql($start_date);
$end_date = format_datetime_mysql($end_date);
$insert = $dbh->exec("INSERT INTO calendar(start_date, end_date, notes, category_id, customer_id, added_by, booked_by, booked_for, date_added) VALUES ('$start_date', '$end_date', '$notes', '$category_id', '$customer_id', '$agent_id', '$booked_by', '$booked_for', '$time')");
if($insert){
$notification_msg[] = array(type=>'alert-success', h4=>'Success!', msg=>'Appointment Created');
push_browser_notify('New appointment booked', format_date($start_date).' - '.get_customer_json('business_name', $customer_id).' ('.get_customer_json('first_name', $customer_id).' '.get_customer_json('last_name', $customer_id).') ', '');
header('Location: ' . $_SERVER['HTTP_REFERER']);
}else{
$notification_msg[] = array(type=>'alert-warning', h4=>'Warning!', msg=>'Appointment NOT Created');
}
}