kent@sadcomputer> nslookup api.slack.com
Server:         127.0.0.53
Address:        127.0.0.53#53

** server can't find api.slack.com: NXDOMAIN

kent@sadcomputer> sudo resolvectl flush-caches
[sudo] password for kent:
kent@sadcomputer> nslookup api.slack.com
Server:         127.0.0.53
Address:        127.0.0.53#53

Non-authoritative answer:
Name:   api.slack.com
Address: 54.203.112.76

kent@sadcomputer> dig api.slack.com

; <<>> DiG 9.11.5-P4-5.1ubuntu2.1-Ubuntu <<>> api.slack.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 30330
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 65494
;; QUESTION SECTION:
;api.slack.com.                 IN      A

;; ANSWER SECTION:
api.slack.com.          49      IN      A       54.203.112.76

;; Query time: 0 msec
;; SERVER: 127.0.0.53#53(127.0.0.53)
;; WHEN: Mon Apr 27 17:10:37 MDT 2020
;; MSG SIZE  rcvd: 58