PHP warning on custom account tab

Hi,
I followed this useful guide to add a custom account tab:
https://www.champ.ninja/2020/05/add-a-custom-account-tab-with-profile-form-fields/

Now on my custom tab page appears a PHP warning:
Warning: foreach() argument must be of type array|object, string given in [PATH]/divi-child/functions.php on line 211

This is the line 211, referring to the link above:
foreach ( $fields as $key => $field ) {

How can I fix it?

Thanks,
Angelo