Custom Avatar via Image leads to blank avatar image

Hi,

I have added a custom avatar to the user profile, like described in https://metabox.io/create-custom-avatar/. Only change I made was that I used Image instead of Single Image, as I don't want the user to access the Media library.

Used the same custom_avatar field id and added the code to functions.php.

But the profile picture ends up as blank image, like this: https://share.getcloudapp.com/rRuG7zO8.

<div>
<?php
add_filter( 'rwmb_meta_boxes', 'your_prefix_register_meta_boxes' );

function your_prefix_register_meta_boxes( $meta_boxes ) {
$prefix = '';

$meta_boxes[] = [
    'title'  => esc_html__( 'Your Profile', 'text-domain' ),
    'id'     => 'user-profile-default-fields',
    'fields' => [
        [
            'id'       => $prefix . 'first_name',
            'type'     => 'text',
            'name'     => esc_html__( 'First Name', 'text-domain' ),
            'required' => 1,
        ],
        [
            'id'   => $prefix . 'last_name',
            'type' => 'text',
            'name' => esc_html__( 'Last Name', 'text-domain' ),
        ],
        [
            'id'       => $prefix . 'age',
            'type'     => 'number',
            'name'     => esc_html__( 'Your Age', 'text-domain' ),
            'min'      => 18,
            'max'      => 100,
            'required' => 1,
        ],
        [
            'id'   => $prefix . 'biography',
            'type' => 'textarea',
            'name' => esc_html__( 'Biography', 'text-domain' ),
            'desc' => esc_html__( 'Tell me about yourself', 'text-domain' ),
        ],
        [
            'id'               => $prefix . 'custom_avatar',
            'type'             => 'image',
            'name'             => esc_html__( 'Your Avatar', 'text-domain' ),
            'desc'             => esc_html__( 'If you have registered with your social media account, I take your avatar from there.<br>You can change it here if you want, or add it here if you registered traditionally.', 'text-domain' ),
            'force_delete'     => 1,
            'max_file_uploads' => 1,
        ],
    ],
    'type'   => 'user',
];

return $meta_boxes;

}
</div>