Following. I have the same issue

I would recommend you use Cloudflare's DNS service as they automatically issue TLS/SSL certificates for free.

https://developers.cloudflare.com/dns/zone-setups/full-setup/setup/

Can you share the screenshot, showing the CNAME and value provided by railway, and the one which you added in your DNS provider?

Here is what I have on the DNS provider:

(Ignore this message)

I figured this out. In this document - https://docs.railway.com/guides/troubleshooting-ssl#certificate-stuck-on-validating-challenges - I read the part about CNAME flattening but I didn't think it applied to me. It does - and it probably applies to most Railway users.

My DNS provider, porkbun.com, supports CNAME flattening. I followed their instructions to add a CNAME flattening ALIAS record ("sharkwar.studio", providing the railway URL as the answer), then changed the CNAME record to "www.sharkwar.studio" (also with the railway URL as the answer). I waited 12 hours for the DNS records to propagate, clicked the Try Again button, and everything worked. For a Django app like mine, remember to add your new domain name to ALLOWED_HOSTS and CSRF_TRUSTED_ORIGINS.

To be honest, I kind of stopped troubleshooting this when I saw the "An internal error occurred" message and noticed a bunch of other posts on the same topic. That error message means something to a developer -- usually that there's a bug in whatever service you're calling. With a more specific error message I likely would have kept digging and arrived at this solution sooner.