Hi @houami
your command says, you want to create a certificate with "dsag.tk, *.dsag.tk".
So it's unrelevant that you use https://3-18-215-34.nip.io:3080
ns-1333.awsdns-38.org is one of your name servers - see dsag.tk - Make your website better - DNS, redirects, mixed content, certificates - the name server part.
There you have to create the two required TXT records `_acme-challenge.dsag.tk' - two entries with the same domain name, but different values.