Ajax Post error 500 ONLY when passing any data - ajax

Question

The error occurs only when I pass any
data : ,
to my ajax. I tried to put it in the URL, in an array, change the name, ... nothing change the result. If I remove data, I got a proper 200 status response.
If I access directly the page, no problem, still a clean 200.
My ajax function :
$( "#deleteMool" ).click(function() {
$.ajax({
url : '/Trunk/SofastBS/mool-delete',
type : 'POST',
data : 'mool=' + '4' ,
dataType : 'html' ,
success : function(code_html, statut){
if (code_html == 'OK') {
location.reload();
}
},
});
});
My PHP page :
<?php
$ID = $_POST['mool'];
// Check if user is logged in
if ( is_user_logged_in() ){
/*.................. Empty request block ...............*/
if ($ID != ''){
$mool_id = delete_mool( $ID ) ;
//On success
if ( $mool_id == true ) {
echo 'OK';
}
else{
echo 'Une erreur est survenue.';
}
}
else {
header('Location: '.site_url());
echo 'ID EMPTY';
}
}
else {
header('Location: '.site_url());
echo 'NOT LOGGED IN';
}
My HEADERS :
Response header :
HTTP/1.0 500 Internal Server Error
Date: Tue, 29 Oct 2019 10:19:37 GMT
Server: Apache
Expires: Wed, 11 Jan 1984 05:00:00 GMT
Cache-Control: no-cache, must-revalidate, max-age=0
Link: <http://192.168.1.95/Trunk/SofastBS/wp-json/>; rel="https://api.w.org/"
Link: <http://192.168.1.95/Trunk/SofastBS/?p=400>; rel=shortlink
Content-Length: 1
Connection: close
Content-Type: text/html; charset=UTF-8
Request header :
POST /Trunk/SofastBS/mool-delete HTTP/1.1
Host: 192.168.1.95
Connection: keep-alive
Content-Length: 6
Accept: text/html, */*; q=0.01
Origin: http://192.168.1.95
X-Requested-With: XMLHttpRequest
User-Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
Referer: http://192.168.1.95/Trunk/SofastBS/mool/
Accept-Encoding: gzip, deflate
Accept-Language: fr-FR,fr;q=0.9,en-US;q=0.8,en;q=0.7
Cookie: wordpress_test_cookie=WP+Cookie+check; wordpress_logged_in_censored_by_me; wp-settings-1=mfold%3Do; wp-settings-time-1=1572342088; PHPSESSID=65hhsmd6290lrei04se2tc8c93
In order to compare, I use the same bit of code in another web part, on another site, and work flawlessly :
Here are the headers from the working bit :
Response header :
HTTP/1.1 200 OK
Date: Tue, 29 Oct 2019 10:29:38 GMT
Server: Apache
Expires: Wed, 11 Jan 1984 05:00:00 GMT
Cache-Control: no-cache, must-revalidate, max-age=0
Link: <http://192.168.1.95/trunk/nagacount/wp-json/>; rel="https://api.w.org/"
Link: <http://192.168.1.95/trunk/nagacount/?p=79>; rel=shortlink
Content-Length: 2
Keep-Alive: timeout=5, max=95
Connection: Keep-Alive
Content-Type: text/html; charset=UTF-8
Request header :
POST /trunk/nagacount/mool-delete HTTP/1.1
Host: 192.168.1.95
Connection: keep-alive
Content-Length: 5
Accept: text/html, */*; q=0.01
Origin: http://192.168.1.95
X-Requested-With: XMLHttpRequest
User-Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/77.0.3865.90 Safari/537.36
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
Referer: http://192.168.1.95/trunk/nagacount/mool/
Accept-Encoding: gzip, deflate
Accept-Language: fr-FR,fr;q=0.9,en-US;q=0.8,en;q=0.7
Cookie: wordpress_test_cookie=WP+Cookie+check; wordpress_logged_in_censored_by_me; PHPSESSID=65hhsmd6290lrei04se2tc8c93
I'm stuck on this for a moment, I'm sure I miss something, but I can't find it out. Any hints ?