I have Draytek 2830n , 4 LANS/VLANS, Ubiquiti Edgemax 48 , PCs and VOIP Phones.
All working perfectly with my LAN/VLAN before the changes.
I wished to change my IP and Gateway/IP Address from 172.16.8.253 to 172.16.8.0 as per the URL below (in 2 places). No VLAN changes.
The PCs were fine - all good.
However...the Yealink VOIP phones would not register. Further checks revealed they were receiving an IP but the Gateway was 0.0.0.0. Another phone received the Gateway but would still not register. A VOIP phone from a different provider had same issue. Same problem with WIFI devices (via Ubiqiuti APs) Rebooted everything and same problem. But Desktop PCs were fine without issue!

This was my first attempt at using a /23 network with subnet mask 255.255.254.0
I may have done something incorrect - but if the PCs work fine and receive the Gateway, why would WIFI devices and Voip phones refuse to play ball?
Switched back to 172.16.8.253 for both IP and Gateway and everything was perfect.
I have 3 other LANs on same router with x.x.x.253 as the Gateway - All working fine.
Do realise this device should be upgraded but would still appreciated any thoughts.

https://drive.google.com/file/d/134Heonuf_8fD3CzpFV3lazLQsXvUxOGg/view?usp=share_link