I have built a website with your theme that includes on page navigation as well as navigation from other pages.
I use your navigation manual:
but I have the following isseu:
Please provide us with WP Dashboard and FTP login credentials to the mentioned site in private answer to check the issue.
Please take our apologies for delay in reply, it's due to ticksy maintenance issue.
As I see you are using old theme and core plugin version. Please update them to the latest ones and after check one page navigation.
You can refer to the theme documentation about updating process here