FB Pixel: Problem with IP address in production mode

Question

I'm currently setting up the FB Pixel for the first time (next.js). In development mode everything is working as expected and correctly.

My problem is production mode: I found out that the user ip address is somehow different in browser and server. When I hardcode an ip address, the tracking and deduplication works fine. But as soon as I get the value from server side props (header "x-forwarded-for"), the events from browser and server are tracked (event id is the same, user agent and ip are also passed) - but not deduplicated. By trying and playing with the code I found out that the ip address must be the issue.

Here is some relevant code:

//page.js
export async function getServerSideProps(context) {
  const { req } = context;
  const ip = req.headers["x-forwarded-for"];
  const ua = req.headers["user-agent"];
  return {
    props: {
      ip,
      ua,
    },
  };
}

//and then use the props like so:
  let values = {};
  values.ip = ip;
  useEffect(() => {
    fbTriggerViewContent(values);
  }, []);
  
  
//fbTriggerViewContent.js
const createSendingData = async (values, eventId) => {
  return {
    event_name: "ViewContent",
    event_id: eventId,
    event_time: Math.floor(Date.now() / 1000), 
    action_source: "website",
    event_source_url: window.location.href,
    user_data: {
      client_user_agent: values.ua,
      client_ip_address: "192.158.1.38"
        /* process && process.env.NODE_ENV === "development"
          ? "192.158.1.38"
          : values.ip, */
    },
  }; 
}; 

export default async function fbTriggerViewContent(values) {
  const additionalData = {};

  const eventId = crypto.randomUUID();

  const sendData = await createSendingData(values, eventId);

  fbq.event("ViewContent", additionalData, { eventID: eventId });

  axios({
    url: `https://graph.facebook.com/v20.0/${process.env.NEXT_PUBLIC_FB_PIXEL_ID}/events?access_token=${process.env.NEXT_PUBLIC_FB_ACCESS_TOKEN}`,
    method: "POST",
    headers: {
      "Content-Type": "application/json",
    },
    data: {
      data: [sendData],
      test_event_code: process.env.NEXT_PUBLIC_TEST_ID,
    },
  }).then((response) => response);
}

Can anyone help me with this issue?