This matches a known pattern, not a bug in your backend or Railway's DNS setup: mobile carriers (most commonly reported here: Jio) intercept or block resolution for Railway's shared *.up.railway.app domain at the network level, independent of what the actual DNS records say. It's not unique to this app — the same shared-wildcard-domain blocking has been reported against other platforms on the same carriers (e.g. Supabase's *.supabase.co), which is why desktop/Wi-Fi/other-carrier users are unaffected while specific cellular networks fail outright with ERR_NAME_NOT_RESOLVED.

Your DNSChecker result doesn't contradict this — propagation and carrier-level filtering are separate layers. DNSChecker queries from generic hosting/resolver infrastructure, not through an actual SIM on the affected carrier, so it can show clean global propagation while that carrier still blocks the domain for its own subscribers.

Reference: a near-identical report resolved here — same fix worked both times:

Get a cheap custom domain (a $1–2/year .xyz is enough) and point it at your Railway service, proxied through Cloudflare — meaning Cloudflare's orange-cloud/proxy mode, not just Cloudflare as your registrar's nameservers. That matters: the block is tied to Railway's shared domain/IP reputation, so a plain CNAME straight to Railway doesn't help — you need traffic actually terminating on Cloudflare's IP space in front of Railway.

Since this is a backend API URL baked into a mobile app rather than a public web page, this is a low-friction fix: add the custom domain in Railway (Settings → Networking → Custom Domain), set it up proxied through Cloudflare, then point the app's API base URL at the new domain and ship an updated build to your Closed Testing group. No need to wait on Railway for this one — it isn't something they can fix on their end, since it's filtering happening inside the carrier's network, outside Railway's infrastructure.

One cheap thing worth checking in parallel: Railway's status page has a "DNS Resolution Failures" incident category — worth a quick look in case there's also something platform-side happening concurrently, though the symptom pattern here (specific carriers only, not all mobile users) points at carrier-side blocking as the primary cause.

If you can get the carrier name(s) from your affected testers (Settings → About Phone → Network on Android, or just ask them), that'll confirm it definitively and help the next person who finds this thread.

Same caveat as before: no live URL for this ticket, so I can't confirm it's actually on the Bounty Board or still open — send the link if you want me to check status before it's posted.

Sources:

My website users are facing issues with Jio network while accessing – Railway Central Station

Supabase down on JIO ISP · Issue #43142