You’ll probably have to wait for an update, unless you’re comfortable with writing a fix yourself (I’m not familiar with DirectAdmin, so can’t really give you any pointers, sorry).
For a more thorough explanation, take a look at this post. Basically, Let’s Encrypt changed the subscriber agreement. Clients that are fully compliant with ACME are able to handle this, but it looks like DirectAdmin hardcoded the agreement URL and that broke code that generates new ACME accounts.