I've been struggling for a long time with Chrome Extensions. How do I get the URL of the tab from background.js (my service worker) ?

It seems like a very easy thing to do but........

// manifest.json
{
  "name": "Getting Started Example",
  "description": "Build an Extension!",
  "version": "1.0",
  "manifest_version": 3,
  "background": {
    "service_worker": "background.js"
  },
  "permissions": ["storage", "activeTab", "scripting"],
  "action": {
    "default_popup": "popup.html"
  }
}

// background.js
chrome.tabs.onActivated.addListener(activeInfo => {
  chrome.tabs.get(activeInfo.tabId, (tab) => {
    // tab.url is undefined, it should not.
  });
});

it doesn't work. why ?