Web Cert - ACME / DNS-01 / Cloudflare - Still trying to hit well known URL

Using ACME 3.0.6-3, acme-dnsapi on 22.03.

Cloudflare API key etc set up and working fine - this part appears to work, however during the process of trying to request the certificate, something seems to be hitting the well-known at the routers hostname, which AIUI shouldn't be nessecary with DNS-01

Wed Aug 30 14:16:06 2023 daemon.err run-acme[2126]: router.svc.blahblah.me:Verify error:2606:4700:3031::ac43:d51b: Invalid response from http://router.svc.blahblah.me/.well-known/acme-challenge/blahblahblah: 522

My understanding is that this shouldn't be necessary, and should be handled by a TXT record via the CloudFlare API (as is the whole point of DNS-01).

Am I misunderstanding this or is there an issue in the implementation here?