NC from snap - enable-https error

I try to enable https on a snap installation (ubuntu 14.04)

sudo nextcoud.enable-https lets-encrypt

basically throws …

Type: unknownHost
Detail: No valid IP addresses found for

… at me. I can reach my nc instance through that domain though as while https is not yet enabled. Likewise I can’t draw much sense from that error.

Anyone with ideas how to solve this?