According to this page: DNS providers who easily integrate with Let's Encrypt DNS validation - Issuance Tech - Let's Encrypt Community Support (letsencrypt.org)
You might have to switch ACME clients to get DYNU API plugin support.
From certbot to acme.sh 
Still looking...
I would try using the RFC2136 plugin:
Welcome to certbot-dns-rfc2136’s documentation! — certbot-dns-rfc2136 0 documentation
If that fails, the path of least resistance is installing acme.sh.
[not about to write a new plugin ]