Glitch domain and my custom domain aren't syncing

Hi,
I made an app in Glitch with Node.js. And I setup a custom domain for it (onclass.tk). Now I’m going to get a SSL certificate for it with certbot(Let’s Encrypt). Then I changed my 404 page to the text given by the certbot and returned the status code 200 instead of 404. When I view my site with the glitch url (something like: https://onclass.glitch.me/.well-known/acme-challenge/key), it worked. But when I view it in my custom domain (something like: http://onclass.tk/.well-known/acme-challenge/key) it doesn’t work anymore. It’s sending me error 404. Can anyone help me?

Thanks

Ihighly recommend you use Cloudflare as it comes with a free certificateand ddos protection.

But I need to use a secured WebSocket connection. So I need a certificate for it.

Cloudflare gives you that too.

To @ChalanaN’s point, Cloudflare only provides HTTPS between the visitor and Cloudflare, not between Cloudflare and the server.

But how can I get the .pem file and the key?