.

The CNAME and the ownership check are two separate things here.

For aicoach.ultimateonlinemastery.org, the CNAME is already pointing at Railway:

aicoach.ultimateonlinemastery.org -> v0cwpoyh.up.railway.app

But the ownership TXT record is not visible:

_railway-verify.aicoach.ultimateonlinemastery.org -> no TXT record

That would explain why the domain can look propagated but still stay in VALIDATING_OWNERSHIP.

I would fix it in this order:

1. In Railway, open the custom domain entry for aicoach.ultimateonlinemastery.org.
2. Copy the exact TXT host and value Railway shows.
3. In the DNS zone for ultimateonlinemastery.org, add that TXT record at the exact host.

For this subdomain, the host will usually be:

_railway-verify.aicoach

not:

_railway-verify.aicoach.ultimateonlinemastery.org.ultimateonlinemastery.org

and not just:

_railway-verify

Your authoritative nameservers are:

dns1.registrar-servers.com
dns2.registrar-servers.com

so make sure the TXT record is added in the DNS panel that controls those nameservers. Adding it in another DNS provider will not help unless the nameservers are changed to that provider.

After saving, check these two records:

dig CNAME aicoach.ultimateonlinemastery.org +short
dig TXT _railway-verify.aicoach.ultimateonlinemastery.org +short

The first should return the Railway target, and the second should return the Railway verification value. Once both are visible from DNS, go back to Railway and retry verification.

I would avoid deleting and re-adding the domain repeatedly while testing. That can rotate the Railway target or verification token and make the DNS records you just added stale. Keep the current domain entry, add the missing TXT record exactly as shown, then verify again.