Thank you for asking this question in the support community. The custom DNS (and other dynamic DNS) feature is explained in the Configuring Dynamic DNS in AOS - Quick Configuration Guide?
Please, let me know if you have additional questions about your application or about the guide.
As described in No-IP documentation, request should look like standart HTTP request:
I cant set Username or Password option in Custom dynamic DNS within AOS, and if I set plain text request - I have no IP-address variable, and dont know how AOS compose server request.
I found no such information in presented manual.
Thank you for helping