Simple PDO select statement not working

Question

I'm not a PHP developer, but having a huge amount of trouble trying to do simple things in this language. The current issue is that I am simply just trying to make a select statement, that works fine if I do it like this:

$sql = "SELECT * FROM victim WHERE steamId = 129847129847"

The rest of my logic runs:

$stmt = $this->pdo->prepare($sql);
$stmt->execute();
$user = $stmt->fetch();
if($user) {
  //success
  error_log('hit');
} else {
  error_log('error????????????');
}

And I get the hit in my console. Great, but that's not very useful. I want to simply just exchange the hardcoded value to something I am passing in the function.

function checkIfVictimExists($steamId)

Now I don't have ALL the code I've tried, but I've just about tried every flavor of this that I've seen on the internet and it continously hits the else no matter what I do. Again, hardcoding the steamId, works fine, trying to inject a value does not work.

Here's my current implementation that is not working:

$sql = "SELECT * FROM victim WHERE steamId = ?";
$stmt = $this->pdo->prepare($sql);
$stmt->execute(array($steamId));
$user = $stmt->fetch();
if($user) {
  //success
  error_log('hit');
} else {
  error_log('error????????????');
}

I know I've tried to pass it in via:

...WHERE steamId = :steamId and ...execute(array(':steamId' => $steamId);

with no luck.

I've simply just tried to add it onto the string, as such:

...WHERE steamId = {$steamId}

AND

...WHERE steamId = ".$steamId."

AND

...WHERE steamId = ".$steamId (thought maybe I needed an extra "?)

Literally nothing works. When I try to get error info, via $this->pdo->errorInfo() all I get is an array like this:

[0] = 0000 [1] = [2] =

Really at a loss for words why this would be so confusing, but obviously I am missing something that I fail to see in any of the google searches I've done. Looking for some help here now, thanks in advance.

EDIT

here is my connection logic:

...
  private $pdo;

  function __construct() {
    $dsn = "mysql:host=".$this->dbhost.";dbname=".$this->dbname.";charset=".$this->charset;
    try {
      $this->pdo = new PDO($dsn, $this->username, $this->password);
      $this->connectionStatus = true;
    } catch(Exception $ex) {
      error_log('Could not connect to DB'.$ex);
    }
  }