Curl api on for loop doesn't work

API
2

Your PHP is bad for want of better wording.

Try something more akin to

include("channels_list.php");

// play call API 

foreach ($channels as $chans) {
    $callAPI = implode('&user_login=', $chans);
    $url="https://api.twitch.tv/helix/streams?user_login=" . $callAPI;
    $ch = curl_init();
      
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
    curl_setopt($ch, CURLOPT_URL,$url);
    curl_setopt($ch, CURLOPT_HTTPHEADER, array(
      'Client-ID: c533u8ntdp29h42xxzwfe0pf5v66dm'
  ));

  $result = curl_exec($ch);
  $i = curl_getinfo($ch);
  curl_close($ch);

  $str = json_decode($result, true);
  if ($i['http_code'] == 200) {
    // play print API
    // do stuff with $str has chnanels
  } else {
    // non 200 do somethign with the error
    // do stuff with $str has error message
  }
}
// end call API


$channels = array(
  array(),
  array(),
  array(),
  array(),
  array()
);

  $canale = "SELECT * FROM `ttp_tsp` ORDER BY id ASC LIMIT 0, 100";
  $result = mysqli_query($connString, $canale)or die(mysqli_error());
  if (mysqli_num_rows($result) > 0){
while($row = mysqli_fetch_assoc($result)){
  $channels[0][] = $row['canale'];
}
  }

  $canale = "SELECT * FROM `ttp_tsp` ORDER BY id ASC LIMIT 100, 100";
  $result = mysqli_query($connString, $canale)or die(mysqli_error());
  if (mysqli_num_rows($result) > 0){
while($row = mysqli_fetch_assoc($result)){
 $channels[1][] = $row['canale'];
}
  }

$canale = "SELECT * FROM `ttp_tsp` ORDER BY id ASC LIMIT 200, 100";
$result = mysqli_query($connString, $canale)or die(mysqli_error());
if (mysqli_num_rows($result) > 0){
    while($row = mysqli_fetch_assoc($result)){
 $channels[2][] = $row['canale'];
}
  }

$canale = "SELECT * FROM `ttp_tsp` ORDER BY id ASC LIMIT 300, 100";
$result = mysqli_query($connString, $canale)or die(mysqli_error());
if (mysqli_num_rows($result) > 0){
    while($row = mysqli_fetch_assoc($result)){
 $channels[3][] = $row['canale'];
}
  }

$canale = "SELECT * FROM `ttp_tsp` ORDER BY id ASC LIMIT 400, 100";
$result = mysqli_query($connString, $canale)or die(mysqli_error());
if (mysqli_num_rows($result) > 0){
    while($row = mysqli_fetch_assoc($result)){
 $channels[4][] = $row['canale'];
}
  }

Also removed the accept header thats not needed with Helix.and added a curl 200 check.