The IP Update API is described as legacy and the REST-API should be preferred according to the docs. However, when you have to update your IP, you want short TTLs which the normal API does not allow.
I saw the offer to request shorter TTLs, but the normal API does not seem to be a full replacement with the defaults yet because short TTLs are a big point of DynDNS.
So is the IP Update API eventually not legacy?
I think that is somewhat unfortunate wording in the documentation. I don’t think the IP Update API will go away anytime soon.
And as you noted, it is currently the only way to to get DynDNS RRsets to have the low TTL values.
So file a PR if it bothers you 
fiwswe
Well, it does raise the question, if a lower TTL is acceptable, why does the “normal” API not allow this? 
Hi H_D,
Welcome to deSEC! 
Because the dynDNS interface, including the low TTL, is restricted to A/AAAA records, whereas the general API treats all record types the same. However, we don’t want people to create PTR records etc. with 60s TTLs, as that would most likely be a misunderstanding.
Perhaps we should stop calling the dynDNS interface “legacy”. OTOH, it supports plain HTTP, which is really something from the past. So we’ve stuck the label to it to convey the impression that it’s not a state-of-the-art protocol. 
Stay secure,
Peter
Hi Peter,
thank you for clarifying this, it’s totally understandable.