Your custom domain is missing both required DNS records, which is why it has been stuck. You need to add two records at your domain registrar: a CNAME record pointing to the target shown in the domain's entry under your service's Settings (Networking section), and a TXT record with name _railway-verify and value railway-verify=fe8016564a96dfbc4ed3f99c66586eb298407c9fca6baa526e130a6c25ab64cd. Once both records propagate, verification and certificate issuance will resume on their own.