GitLab package manager adds WebKitFormBoundary inside my files

I've built a small HTML/JS page that uses GitLab API to upload files into the Package Registry like:

<input class="form-control mb-1" type="file" id="formFile" />
<button class="btn btn-primary w-100" onclick="Send();">
<script>
function Send() {
...
var formData = new FormData();
      formData.append("file", select_file);

      fetch(file_string, {
        method: "PUT",
        headers: {
          "PRIVATE-TOKEN": GITTOKEN,
        },
        body: formData,
      })
        .then((response) => response.json())
        .then((data) => {
...

I've noticed that, for some reason, if I upload a text file like crc.txt which contains just a CRC code like ac8daadc, GitLab seems to write the payload/content of the file like:

------WebKitFormBoundaryVPZEUt253yBGuPTN
Content-Disposition: form-data; name="file"; filename="crc.txt"
Content-Type: text/plain

ac8daadc
------WebKitFormBoundaryVPZEUt253yBGuPTN--

Why is that? Can I keep the original payload?

It turned out that the issue was on the var formData = new FormData();formData.append("file", select_file); code.

The formData not only upload the data, but serialize other information into the file, corrupting it.

Passing the file directly with

      fetch(file_string, {
        method: "PUT",
        headers: {
          "PRIVATE-TOKEN": GITTOKEN,
        },
        body: select_file,
      })

worked