It’s garbage.
Noip is recommended here often and has free option as well (of course, it’s only free if time is worthless – they want you jump through hoops monthly to keep it free).
If you have your own domain, your registrar may offer DDNS at no cost, or provide API you can use with some utilities. (For example, my domains are on Cloudflare, so I let inadyn update the A record programmatically. Because it’s cloudflare – it is rock solid.)
Generally, I would avoid free options. They usually turn out to be very expensive. For example, consider amount of time you have already spent debugging this issue, just because of illusion of “free” service. Paying $2 would be much cheaper.