When connecting the certificate through ISP Manager, I selected confirmations via DNS. The panel issued the following message:
To continue the procedure of obtaining the certificate Let's Encypt sub.domain.ru_sert1 add TXT records:
'_acme-challenge.sub.domain.ru. TXT T4Fk9N0KCLiJelOcXjE_ycCLK8SwVaqAFHYoCt0sEn8, _acme-challenge.www.sub.domain.ru. TXT SPeLDqoQzM6ffO3LzKiTlvLS6OoO7yRsBWXWDMhzKtM '
on the name servers 'dns1.hoster.net., dns2.hoster.net., dns3.hoster.net.'. Receipt will be resumed after 2018-06-10 16:34:04
Message punctuation saved.
Question: This is what the interface for creating a new DNS record looks like. 
Type - txt is clear.
In the name of what to write? _acme-challenge.sub.domain.ru. or T4Fk9N0KCLiJelOcXjE_ycCLK8SwVaqAFHYoCt0sEn8
In the address to write dns1.hoster.net. or something from what is higher? If so, then one will be enough, or do you need all 3?
hostname mode value. - user207618_acme-challenge.sub.domain.ru.? mode txt and value isT4Fk9N0KCLiJelOcXjE_ycCLK8SwVaqAFHYoCt0sEn8? - DrZorg