XMLHttpRequest FormData not submitting data

I am trying to submit a form using the post method and a FormData object. I annotated my servlet with @MultipartConfig but it doesnt work

js

async function addAuthors() {
        let xhr = new XMLHttpRequest();
        const form = document.getElementById( "authorForm" );
        const FD = new FormData(form);
        xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
        xhr.open("POST", "http://localhost:8081/Task1_war/main?command=addAuthor");
        xhr.send(FD);
} 

html

   <form id="authorForm">
        <Label>Author (required)</Label>
        <input type="text"  name="authorName" class="req"/>
        <label class="errorInput"  ></label>
        <Label>Author image></Label>
        <input type="file" id="authorImage" name="path" accept=".jpg,.png,.jpeg ">

    </form>
    <div class="add" onclick="addAuthors()">Send</div>