I’m building a multi-tenant SaaS app, and I need help figuring out how to handle dynamic custom subdomains.

Here’s the situation:

• My main web app is hosted on a custom domain connected to Railway, for example:

• I’d like my users to be able to connect their own subdomains to it, like:

  dashboard.customer.com → CNAME → app.myapp.com
  

• When someone visits dashboard.customer.com, I want Railway to serve the same app (my backend detects the tenant based on the Host header).

Right now, if I try this, I get the “Train has not arrived at the station” message — which I understand means Railway doesn’t recognize the domain until it’s manually added under Settings → Networking → Custom Domains.

That works for testing, but in production this won’t scale. I need a setup where customers can connect their own subdomains automatically (like other SaaS platforms that use wildcard or dynamic domain mapping).

So my questions are:

1. Does Railway support dynamic custom domains - so any CNAME pointing to my base domain is accepted automatically?

2. If not, is there an API or programmatic way to register new custom domains from my app when a customer adds theirs?

I’m basically trying to let customers point subdomain.theirdomain.com → app.myapp.com and have it just work, without manually adding every new domain inside Railway.

Thanks so much for any clarification or suggestions!