@shorthouse06 

you are right, you can only have one on each wan interface, why it is limited to only one I don't know

Thank you very much for confirming!

Seems strange to me that this isn't allowed, I wonder if this is a bug or a design oversight?

I don't see why it shouldn't be possible to set up multiple DDNS for a single interface - as far as I understand it all the DDNS setup does is basically make CURL requests, so I can't see a technical reason why multiple for the same interface shouldn't be allowed?

Perhaps the developers thought nobody would want multiple domains pointing to the same IP? I am trying to run two services with two subdomains pointed at my router, so this functionality would be very useful for me... I can't imagine this is too much of an obscure usecase? Especially if you were doing something like virtual hosting for a bunch of websites.

  @Hank21 Hi, thanks for your reply

It's from the same provider, I'm on the Custom DDNS page where only one provider URL can be entered at the top. I don't have any other DDNS configuations on the other pages.

I have a single Custom DDNS already set up, and then when I go to create another one (from the same provider (e.g. the same URL)) I get the error in the screenshot.