How to force to make HTTP requests from a frontend running on HTTPS?

I have a frontend running on HTTPS locally with a local certificate. I'd like to hit a local backend that is on HTTP.

I added the meta tag to my index.html to allow for this:

<meta http-equiv="Content-Security-Policy" content="upgrade-insecure-requests">

...but axios refuses to do it:

        axios({
            method: 'post',
            baseURL: 'http://localhost:3000',
            url: '/test',
            data: {
                firstName: 'Will',
                lastName: 'Smith'
            }
        }).then((result) => {
            console.log('done!');
        }

Note that I explicitly add http to the baseUrl. Still, I get this:

POST https://localhost:3000/test net::ERR_SSL_PROTOCOL_ERROR

Axios still sends through https.

I tried using fetch:

       fetch('http://localhost:3000/test', {
            method : "POST",
            body: JSON.stringify({
                firstName: 'Finn',
                lastName: 'Williams'
            }),
        }).then((response) => {
            console.log('done! ' + response.json());
        ).catch((error) => {
            console.log('error');
        });

Then finally a raw XMLHttpRequest request:

        const http = new XMLHttpRequest();

        http.open("POST", 'http://localhost:3000/test', true);

        // Call a function when the state
        http.onreadystatechange = function () {
            if (http.readyState == 4 && http.status == 200) {
                alert(http.responseText);
            }
        }
        http.send(JSON.stringify({
            firstName: 'Finn',
            lastName: 'Williams'
        }));

But every time the browser seems to switch to HTTPS and it fails with that same error.

Is it possible to make this happen?