When making a chrome extension, I keep getting this error

Uncaught (in promise) Error: Could not establish connection. Receiving end does not exist.

Along with

background.js:0 (anonymous function)

Does anyone know how I could resolve this? I literally have like 3 lines in both my files.

This is my background.js file

chrome.tabs.onUpdated.addListener((tabId, tab) => {
  if (tab.url && tab.url.includes("linkedin.com/in")) {
    chrome.tabs.sendMessage(tabId, {type: "MAIN", profile: "test"});
  }
});

and This is my ContentScript.js file

(() => {
    chrome.runtime.onMessage.addListener((obj, sender, response) => {
        //const { type, profile } = obj;
        response = {line1 : "hello"}
    });
})();

Any help would grealy be appreciated :)