I have a Chrome Extension that is trying to send data to a Laravel API on a different domain but the data is empty in the API

Question

I set up a brand new Laravel backend without any middleware/CORs and a simple Chrome Extension to detect the clicking of a button on one domain and then send a message to the Laravel backend in the new Laravel backend. When dumping request()->all() I just get an empty array.

I also tried setting it so that clicking the button on domain-a would send the data to domain-b and the data was seen by domain-b.

Here's the manifest.json:

{
    "name": "Test",
    "description": "Top Secret",
    "version": "0.1.0",
    "manifest_version": 3,
    "background": {
        "service_worker": "background.js" // This is empty
    },
    "content_scripts": [
        {
            "matches": ["http://domain-a.test/*"],
            "js": ["script.js"]
        }
    ],
    "externally_connectable": {
        "matches": ["http://domain-b.test/*/"]
    },
    "host_permissions": [
        "http://domain-b.test/"
  ]
}

Here's my Chrome extension content_script:

let element = document.getElementById('a-button-yo');
if (element) {
    console.log('setting listeners');
    element.addEventListener('click', event => {
        fetch('https://domain-b.test/api/test_it', {
            method: 'POST',
            mode: "no-cors",
            headers: {
              "Content-Type": "application/json",
              // 'Content-Type': 'application/x-www-form-urlencoded',
            },
            body: {message: 'The button was clicked.'}
        });
    });
}```