wp_handle_upload during WordPress theme development

So I’m building my own WordPress theme and I included a setting to be able to change the sites logo.

This is the part that registers the function that handles the upload:

add_settings_field("logo", "Logo", "logo_display", "theme-options", "section");
register_setting("section", "logo", "handle_logo_upload");

This is the handler function that is supposed to handle the file given:

function handle_logo_upload()
{
    if ( ! function_exists( 'wp_handle_upload' ) ) {
        require_once( ABSPATH . 'wp-admin/includes/file.php' );
        }

        $uploadedfile = $_FILES['file'];

        $upload_overrides = array( 'test_form' => false );

        $movefile = wp_handle_upload( $uploadedfile, $upload_overrides );

        if ( $movefile && !isset( $movefile['error'] ) ) {
            echo "File is valid, and was successfully uploaded.\n";
            var_dump( $movefile);
        } else {
            /**
             * Error generated by _wp_handle_upload()
             * @see _wp_handle_upload() in wp-admin/includes/file.php
             */
        echo $movefile['error'];
    }

    return 'stringaz';
}

This is what the theme panel looks like: https://pasteboard.co/uwC3Qmi.png

Here you can see that the handler is not working because a string called ‘stringaz’ is being presented where the logo should appear: https://pasteboard.co/vsnqkay.png

What do I need to change to the handler function to get this code to run?

cheers!