Many thanks for the reply. I’ve installed curl - however when testing my script in certify it just seems to pull down the content of the freedns page and my TXT record is not created.
Clearly there is something amiss in my syntax - I’ve inputted the dns_cookie correctly and my data_id is set correctly for the subdomain in question.
Here’s the FAQ on the freedns site for reference.
https://freedns.afraid.org/faq/#17
Any ideas?