I am trying to send a message from my background script to my content script. Every time I load the extension, I immediately get these two errors in the Service Worker:

Unchecked runtime.lastError: Could not establish connection. Receiving end does not exist.

followed by

Error handling response: TypeError: Cannot read properties of undefined (reading 'farewell')
    at chrome-extension://kglmnphkfjhfplfdmjfhegdedeochkmc/background.js:3:28

Here is my code, copied from these Google Chrome Extension developer guides:

https://developer.chrome.com/docs/extensions/mv3/getstarted/

https://developer.chrome.com/docs/extensions/mv3/messaging/

manifest.json

{
    "name": "Getting Started Example",
    "description": "Build an Extension!",
    "version": "1.0",
    "manifest_version": 3,
    "background": {
      "service_worker": "background.js"
    },
    "permissions": ["storage"],
    "content_scripts": [
      {
          "matches": ["<all_urls>"],
          "run_at" : "document_end",
          "js" : ["contentscript.js"]
      }
    ]
  }

background.js

chrome.tabs.query({active: true, currentWindow: true}, function(tabs) {
    chrome.tabs.sendMessage(tabs[0].id, {greeting: "hello"}, function(response) {
      console.log(response.farewell);
    });
  });

contentscript.js

chrome.runtime.onMessage.addListener(
    function(request, sender, sendResponse) {
      console.log(sender.tab ?
                  "from a content script:" + sender.tab.url :
                  "from the extension");
      if (request.greeting === "hello")
        sendResponse({farewell: "goodbye"});
    }
  );

I have tried disabling all of my other Chrome extensions and the problem persists.