Twitter OAuth 2.0 refresh token expired?
It probably was not expiry. It was rotation.

# The scope parameter of your /2/oauth2/authorize URL must include it:
scope=tweet.read%20tweet.write%20users.read%20offline.access

import fs from "node:fs/promises";

const TOKEN_FILE = "./x-tokens.json";
const CLIENT_ID = process.env.X_CLIENT_ID;
const SKEW_MS = 5 * 60 * 1000; // refresh 5 minutes early

let inflight = null; // single-flight: concurrent callers share one refresh

export async function getAccessToken() {
  const tokens = JSON.parse(await fs.readFile(TOKEN_FILE, "utf8"));
  if (Date.now() < tokens.expires_at - SKEW_MS) {
    return tokens.access_token;
  }
  inflight ??= refresh(tokens).finally(() => { inflight = null; });
  return inflight;
}

async function refresh(tokens) {
  const res = await fetch("https://api.twitter.com/2/oauth2/token", {
    method: "POST",
    headers: { "Content-Type": "application/x-www-form-urlencoded" },
    body: new URLSearchParams({
      grant_type: "refresh_token",
      refresh_token: tokens.refresh_token,
      client_id: CLIENT_ID,
    }),
  });
  if (!res.ok) {
    throw new Error(`Refresh failed ${res.status}: ${await res.text()}`);
  }

  const data = await res.json();
  const next = {
    access_token: data.access_token,
    refresh_token: data.refresh_token, // rotated: the old one is dead now
    expires_at: Date.now() + data.expires_in * 1000,
  };
  // Persist BEFORE returning. Crash after refresh but before this
  // write and your stored refresh token is already burned.
  const tmp = TOKEN_FILE + ".tmp";
  await fs.writeFile(tmp, JSON.stringify(next));
  await fs.rename(tmp, TOKEN_FILE);
  return next.access_token;
}

import json, os, time, threading
import requests

TOKEN_FILE = "x-tokens.json"
CLIENT_ID = os.environ["X_CLIENT_ID"]
SKEW = 300  # refresh 5 minutes early
_lock = threading.Lock()

def get_access_token() -> str:
    with _lock:
        with open(TOKEN_FILE) as f:
            tokens = json.load(f)

        if time.time() < tokens["expires_at"] - SKEW:
            return tokens["access_token"]

        r = requests.post(
            "https://api.twitter.com/2/oauth2/token",
            data={
                "grant_type": "refresh_token",
                "refresh_token": tokens["refresh_token"],
                "client_id": CLIENT_ID,
            },
        )
        r.raise_for_status()
        data = r.json()

        tokens = {
            "access_token": data["access_token"],
            "refresh_token": data["refresh_token"],  # rotated
            "expires_at": time.time() + data["expires_in"],
        }
        tmp = TOKEN_FILE + ".tmp"
        with open(tmp, "w") as f:
            json.dump(tokens, f)
        os.replace(tmp, TOKEN_FILE)  # atomic
        return tokens["access_token"]