PHP message: PHP Fatal error: Uncaught TypeError: Cannot access offset of type string on string

function uploadSingleFile($zoneImage, $fileMoveTo, $fileAllowedExtensions, $fileAllowedSize, $zoneCustomer, $zone)
{
    global $config;

    // define file upload settings
    $errors = array();
    $fileName = $zoneImage['name'];
    $fileSize = $zoneImage['size'];
    $fileTmp = $zoneImage['tmp_name'];
    $fileType = $zoneImage['type'];
    $fileExt = strtolower(end(explode('.', $zoneImage['name'])));
    $MBtoByte = $fileAllowedSize * 1048576;
    $extensions= $fileAllowedExtensions;

    // define errors
    if (in_array($fileExt, $extensions) === false) {
        $errors[] = "Dieser Datei-Typ ist nicht erlaubt";
    }

    if ($fileSize > $MBtoByte) {
        $errors[] = 'Die Datei ist zu gross';
    }

    // finally try to upload the file
    if (empty($errors) == true) {
        $temp = explode(".", $zoneImage["name"]);
        $newfilename = $zoneCustomer . '-' . strtoupper($zone) . '-' . uniqid() . '.' . end($temp);

        move_uploaded_file($fileTmp, $_SERVER["DOCUMENT_ROOT"] . $fileMoveTo . $newfilename);
        $status = '1';
    } else {
        $status = '0';
    }

    // build array of the different outputs
    $uploadStatus = array($status, $newfilename, $errors);

    return $uploadStatus;
}

function updateZoneData($zoneFile, $zoneCustomer, $zone, $zoneLink, $maxWidth, $bannerID)
{
    global $db;

    // get customer values
    $getCustomerValues = getColumnValue('customers', "WHERE `customerNr` = '" . $zoneCustomer . "'");

    // define redirect url
    switch ($zone) {
      case "a1":
        $redirectZone = "zones.php#zones-overview-a1-overview";
      break;
      case "a2":
        $redirectZone = "zones.php#zones-overview-a2-overview";
      break;
      case "b1":
        $redirectZone = "zones.php#zones-overview-b1-overview";
      break;
      case "b2":
        $redirectZone = "zones.php#zones-overview-b2-overview";
      break;
      case "b3":
        $redirectZone = "zones.php#zones-overview-b3-overview";
      break;
      case "b4":
        $redirectZone = "zones.php#zones-overview-b4-overview";
      break;
      case "a9":
        $redirectZone = "zones.php#zones-overview-a9-overview";
      break;
      case "a9-1":
        $redirectZone = "zones.php#zones-overview-a9-1-overview";
      break;
      case "a11":
        $redirectZone = "zones.php#zones-overview-a11-overview";
      break;
      default:
        $redirectZone = "zones.php";
      }

    // upload file to the server
    $uploadZoneData = uploadSingleFile($zoneFile, '/adserver/banners/', array("jpg", "jpeg", "png", "gif"), '3', $zoneCustomer, $zone);

    if ($uploadZoneData[1]['size'] != 0) {
        if ($uploadZoneData[0] == '1') {

            // create ZIP-Backup (zone-banners) from '/adserver/banners' to '/cp/includes/files/zip-backups'
            createZipBackup('/adserver/banners', '/cp/includes/files/zip-backups', 'adserver-banners.zip');

            // get zone values & delete old bannerImg from file-system
            $getZoneDeleteValues = getColumnValue('zones', "WHERE `customerNr` = '" . $zoneCustomer . "' AND `zone` = '" . $zone . "' AND `id` = '" . $bannerID . "'");
            unlink($_SERVER["DOCUMENT_ROOT"] . '/adserver/banners/' . $getZoneDeleteValues['0']['bannerImg']);

            // execute action
            $updateZoneData = $db->update("zones", [
                                                   "customerNr" => $zoneCustomer,
                                                   "customer" => $getCustomerValues['0']['customer'],
                                                   "zone" => $zone,
                                                   "bannerImg" => $uploadZoneData[1],
                                                   "bannerLink" => $zoneLink,
                                                   "maxWidth" => $maxWidth,
                                                   "changeDate" => date("Y-m-d H:i:s")
                                                   ], [
                                                      "id" => $bannerID
                                                      ]);

            redirectTo($redirectZone, 1, "« " . strtoupper($zone) . "-Banner (" . $getCustomerValues['0']['customer'] . " [K. N°: " . $zoneCustomer . "]) » wurde erfolgreich aktualisiert.", 'ZONES');
        } else {

        // collect and save errors (file-upload)
            $collectedErrors = array_flatten($uploadZoneData[2]);
            setcookie("collectedErrors", '1', time() + (1 * 5), "/"); // expire in 5 seconds
            $_SESSION["collectedErrors"] = $collectedErrors;

            redirectTo($redirectZone, 0, "« " . strtoupper($zone) . "-Banner (" . $getCustomerValues['0']['customer'] . " [K. N°: " . $zoneCustomer . "]) » konnte nicht aktualisiert werden.", 'ZONES');
        }
    } else {

        // execute action
        $updateZoneData = $db->update("zones", [
                                               "customerNr" => $zoneCustomer,
                                               "customer" => $getCustomerValues['0']['customer'],
                                               "zone" => $zone,
                                               "bannerLink" => $zoneLink,
                                               "maxWidth" => $maxWidth,
                                               "changeDate" => date("Y-m-d H:i:s")
                                               ], [
                                                  "id" => $bannerID
                                                  ]);

        redirectTo($redirectZone, 1, "« " . strtoupper($zone) . "-Banner (" . $getCustomerValues['0']['customer'] . " [K. N°: " . $zoneCustomer . "]) » wurde erfolgreich aktualisiert.", 'ZONES');
    }
}