I just got a notice from Let’s Encrypt Expiry Bot:

Your certificate (or certificates) for the names listed below will expire in 20 days (on 02 Jul 21 11:11 +0000). Please make sure to renew your certificate before then, or visitors to your web site will encounter errors.

I used the following command which I found from DO Questions.

sudo certbot certonly --manual --manual-public-ip-logging-ok --preferred-challenges dns-01 --server https://acme-v02.api.letsencrypt.org/directory -d "*.mydomain.net" -d mydomain.net

But I got the following error:

Press Enter to Continue
Waiting for verification...
Challenge failed for domain mydomain.net
Challenge failed for domain mydomain.net
dns-01 challenge for mydomain.net
dns-01 challenge for mydomain.net
Cleaning up challenges
Some challenges have failed.

IMPORTANT NOTES:
 - The following errors were reported by the server:

   Domain: mydomain.net
   Type:   dns
   Detail: DNS problem: NXDOMAIN looking up TXT for
   _acme-challenge.mydomain.net - check that a DNS record exists for
   this domain

   Domain: mydomain.net
   Type:   dns
   Detail: DNS problem: NXDOMAIN looking up TXT for
   _acme-challenge.mydomain.net - check that a DNS record exists for
   this domain

How can I update Let’s Encrypt?