The same error occurs using letsencrypt instead of Cloudflare API
This configuration is tested and works with several other domains.
traefik | time="2022-02-24T00:34:08Z" level=error msg="Unable to obtain ACME certificate for domains \"myyouniverse.observer,*.myyouniverse.obesrver\" : unable to generate a certificate for the domains [myyouniverse.observer *.myyouniverse.obesrver]: acme: error: 400 :: POST :: https://acme-v02.api.letsencrypt.org/acme/new-order :: urn:ietf:params:acme:error:rejectedIdentifier :: Error creating new order :: Cannot issue for \"*.myyouniverse.obesrver\": Domain name does not end with a valid public suffix (TLD)" providerName=cloudflare.acme