Solved! Attached the sendEmail function to an event and used e.preventDefault() to prevent the default form submission behavior:

emailjs.init({ publicKey: '*' }); 

const sendEmail = (e) => { e.preventDefault();

var emailData = {
    name: 'Konstantinos Iakovou | Web developer',
    notes: 'Check this out!',
};

emailjs.send('service_*', 'template_*', emailData).then(
    (response) => {
        alert('Message successfully sent!');
    },
    (error) => {
        console.error('Failed to send the message:', error);
        alert(`Failed to send the message: ${error.text}`);
    },
);

};