I keep getting "Cannot read properties of undefined (reading 'byteLength')" error when uploading files to a space using aws-sdk for node.js

Hello to all, I’m completely new to Digital Ocean and to cloud storage in general, but even following step by step this tutorial I get the error mentioned in the title. I think that it’s is related to the fact that I’m not authenticated correctly, but I really don’t know why.

The important bits of code are this:

import fs from "fs";
import { S3, PutObjectCommand } from "@aws-sdk/client-s3";

const s3Client = new S3({
  endpoint: "https://fra1.digitaloceanspaces.com",
  region: "fra1",
  credentials: {
    accessKeyId: process.env.SPACES_KEY,
    secretAccessKey: process.env.SPACES_SECRET,
  },
});

and this:

const fileContent = await new Promise((resolve) =>
      fs.readFile("output.webp", (err, data) => resolve(data))
    );
    try {
      const data = await s3Client.send(
        new PutObjectCommand({
          Bucket: "name-of-bucket",
          Key: "test.webp",
          Body: fileContent,
        })
      );
      console.log(
        "Successfully uploaded object: " +
          bucketParams.Bucket +
          "/" +
          bucketParams.Key
      );
      return data;
    } catch (err) {
      console.log("Error", err);
    }

I followed the steps to generate the API keys to access the Space and then I stored them in a .env file, as per this. But I’m not setting anything else, maybe I should, I really don’t know. The SDK version is 3.54.0. Any help would be much appreciated