Firefox extension: Attempting to message content script throws an error

Question

I have spent all day trying to figure this out and I seem to be getting nowhere, can someone share with me where I am going wrong?

I am trying to figure out how to correctly send a message, from a "background" script to a content script. I want to use onBeforeRequest() as the trigger event, so that when it happens a message is to sent to the content script to get some information from the pages DOM.

The DOM part is not present in this example, I am struggling to just establish a working messaging pattern.

manifest file:

{
    "name": "shell",
    "manifest_version": 2,
    "version": "1.0",

    "background": {"scripts": ["background.js"]},
    "content_scripts": [
        {
          "matches": ["<all_urls>"],
          "js": ["content.js"]
        }
      ],
    "permissions": ["tabs","activeTab", "webRequest", "<all_urls>"]
}

background.js file:

activeTab = browser.tabs.query({currentWindow: true,active: true,})

function sendMessageToTabs(activeTab) {
    for (const tab of activeTab) {
      browser.tabs.sendMessage(activeTab.id, { greeting: "Hi from background script" })
         .then((response) => {
            console.log("Message from the content script:");
            console.log(response.response);
         })
         .catch(onError);
    }
 }
browser.webRequest.onBeforeRequest.addListener(sendMessageToTabs, {urls:["https://en.wikipedia.org/wiki/Vehicle"]});

Content.js file:

"use strict";

browser.runtime.onMessage.addListener((request) => {
  console.log("Message from the background script:");
  console.log(request.greeting);
  return Promise.resolve({ response: "Hi from content script" });
});

How to trigger the event

Once I load the extension, I can trigger the on onBeforeRequest() by visiting the Car page of Wikipedia and clicking on the Vehicle part, right under the article profile picture, as shown HERE.

The problem I am having

Is that when the event triggers I get an error in the DevTools console:

TypeError: activeTab is not iterable

I tried a number of ways to solve this issue but it just persists. Any help or pointers would be amazing. Cheers.