Problem with SSL in Digital Ocean when not using DNS by DO

Hi, everyone!

There is a good instruction “Using Custom Domains and SSL with Let’s Encrypt and Traefik”.
I have managed to configure a website on Digital Ocean with it and it works well.

But what if I don’t want to add a domain in DO?
In other words, I don’t want to manage DNS with DO.
I want to keep DNS handling on the domain registrar side. And just make an A-record that points to the DO server.

In this case some problems appear.
Website successfully shown in HTTP. But it seems like Traefik can’t install an SSL-certificate in this case. So no HTTPS.

How can I handle this?