You do not need to change your app's port from 8080. We handle SSL termination and routing at our edge, so your app can listen on any port internally. When you add a custom domain in your service's Settings under Public Networking, you select port 8080 as the target port. Note that Squarespace DNS does not support CNAME flattening, so if you're adding a root/apex domain (e.g., example.com), you would need to either use a subdomain like www.example.com or point your domain's nameservers to a provider like Cloudflare that supports CNAME flattening. Full instructions are in our custom domains guide.

How will I know which Railway DNS servers to point to?

The documentation only provides an example, but not the actual server names.

We don't provide our own nameservers. The suggestion in the previous reply was to point your Squarespace domain's nameservers to Cloudflare (not Railway), since Cloudflare supports CNAME flattening for root/apex domains. You would sign up for a free Cloudflare account, follow Cloudflare's nameserver setup guide to change your domain's nameservers in Squarespace, then create a CNAME record in Cloudflare pointing to the value provided when you add your custom domain in your service's Settings under Public Networking.

i have same issue i changed the subdomain based on your instructions, but txt still has confimred yet, domain became green. i use namecheap

When you click "+ Custom Domain" in your service's Settings under Public Networking and enter your domain, we provide a unique CNAME target value (in the form xxxx.up.railway.app) specific to your service - this is not a static value listed in docs, it is generated per service and displayed in the dashboard at that step. Since Squarespace doesn't support CNAME flattening for root/apex domains, you would need to either use a subdomain (like www.yourdomain.com) or transfer your DNS management to Cloudflare by changing your nameservers, then create the CNAME record there pointing to that value.