The old BytemarkDNS script was quietly deprecated some years ago now (around 2017 if memory serves) as it was being phased out with the ‘new’ control panel version, although it very unlikely that, going to see any development
Behind the scenes the Bytemark DNS platform itself is pretty ancient and even when I was there there was little documentation as to how it actually worked, so it’s likely it’s going to fall over entirely at some point, or have other issues which makes it unusable.
Long term, I’d strongly suggest moving off there when possible - we have a nice web-based platform at Mythic Beasts which has API support and doesn’t require the domain to be registered with us.