Mongoose : Cannot set headers after they are sent to the client

I'm performing a put request on my database, so far everything is working as intended, but I have this annoying message in the console that I believe will hinder my progression.

Cannot set headers after they are sent to the client
[0] (node:13816) UnhandledPromiseRejectionWarning: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

I tried adding an else statement on the ifs and it's doesn't seem to solve the problem? Any ideas ?

A snippet of my code :

// PUT api/requests/upvote/:id
// Upvote or downvote a post
// Private
router.put('/response/upvote/:id/:response_id', auth, async (req, res) => {
  try {
    const request = await Requests.findById(req.params.id);
    //Pull out response

    const array = request.responses.filter((item) => item.id.toString());
    const result = array.find(
      (response) => response.id === req.params.response_id
    );

    if (req.body.vote_type === 'upvote') {
      if (
        result.upvotes.filter(
          (upvote) =>
            upvote.user.toString() === req.user.id &&
            upvote.vote_type === 'downvote'
        ).length > 0
      ) {
        const removeIndex = result.upvotes
          .map(
            (upvote) =>
              upvote.user.toString() === req.user.id &&
              upvote.vote_type === 'downvote'
          )
          .indexOf(req.user.id);

        result.upvotes.splice(removeIndex, 1);

        result.upvotes.push({
          user: req.user.id,
          vote_type: req.body.vote_type,
        });
        await request.save();
        res.json(result.upvotes);
      }

      if (
        result.upvotes.filter(
          (upvote) =>
            upvote.user.toString() === req.user.id &&
            upvote.vote_type === 'upvote'
        ).length > 0
      ) {
        res.status(400).send('You already upvoted this suggestion');
      } else {
        result.upvotes.push({
          user: req.user.id,
          vote_type: req.body.vote_type,
        });
        await request.save();
        res.json(result.upvotes);
      }
    }

    if (req.body.vote_type === 'downvote') {
      if (
        result.upvotes.filter(
          (upvote) =>
            upvote.user.toString() === req.user.id &&
            upvote.vote_type === 'upvote'
        ).length > 0
      ) {
        const removeIndex = result.upvotes
          .map(
            (upvote) =>
              upvote.user.toString() === req.user.id &&
              upvote.vote_type === 'upvote'
          )
          .indexOf(req.user.id);

        result.upvotes.splice(removeIndex, 1);

        result.upvotes.push({
          user: req.user.id,
          vote_type: req.body.vote_type,
        });
        await request.save();
        res.json(result.upvotes);
      }

      if (
        result.upvotes.filter(
          (upvote) =>
            upvote.user.toString() === req.user.id &&
            upvote.vote_type === 'downvote'
        ).length > 0
      ) {
        res.status(400).send('You already downvoted this suggestion');
      } else {
        result.upvotes.push({
          user: req.user.id,
          vote_type: req.body.vote_type,
        });
        await request.save();
        res.json(result.upvotes);
      }
    }
  } catch (error) {
    console.error(error.message);
    res.status(500).send('Server Error');
  }
});