[Nexus]

fetch('https://ipwho.is/?format=json')
    .then(d => d.json())
    .then(res => {
        return fetch('/<your-php-script-address-here>', {
            method: 'post',
            headers: {
                'content-type': 'application/json'
            },
            body: JSON.stringify(res),
        });
    });

PHP:

$receivedIP = $_POST['ip'] ?? null;