ACME client with DynDNS

[SimHat]

I'm looking for someone who has set up the ACME client with DynDNS.org

I use DynDNS.org for my dynamic dns and I'm trying to setup ACME/LetsEncrypt using a DNS challenge.  I've got everything set up, but I have no idea what I need to use for the attached field.  I contacted Dyn support but, unsurprisingly, they weren't much help.

Is there anyone who has done this combination who knows what needs to be used here?  Or maybe there is a way to generate the DNS record from the CLI and just manually enter it in to opnsense.