I'm building a very simple API in PHP to give me data from my DB in application/json format.
Here is my muscular-groups.php file :
<?php
include '../inc/db.php';
if (isset($_GET['id'])) {
    $req = $pdo->prepare('SELECT * FROM muscular_groups WHERE id = ?');
    $req->execute([$_GET['id']]);
    $res = $req->fetchAll();
}
else {
    $req = $pdo->prepare('SELECT * FROM muscular_groups');
    $req->execute();
    $res = $req->fetchAll();
}
header('Content-Type: application/json');
echo json_encode($res);
The problem is that in local all works well as you can see below :

But when I want to access it on my server (at www.example.com/api/muscular-groups), I have a white screen without any error message or error logs.
What is strange : If I replace header('Content-Type: application/json'); and echo json_encode($res); with var_dump($res) in muscular-groups.php, it appears on the screen.
P.S.: very strange, only one of my endpoints works on my server (eg: www.example.com/api/offers) and displays a json output, here's the code :
<?php
include '../inc/db.php';
$req = $pdo->prepare('SELECT * FROM offers');
$req->execute();
$res = $req->fetchAll();
header('Content-Type: application/json');
echo json_encode($res);
I'm lost...
