@Martin_S Maybe worth looking at this thread https://community.tp-link.com/en/business/forum/topic/594038 Whilst its related to an ER605 , I suspect the ER7206 is similar.

@AnnusKhan Currently, the maximum number of clients connected to the network is 345 The default DHCP pool will only provide 253 IP addresses. Whilst I guess you don't have all 345 clients connected...

@Hobbit76 SIP requires a domain That's a new one on me. Is it just a requirement of SIP on the Fritzbox ? At least you have it working now

My understanding of that is, when you configure your LAN, you should provide a DHCP range that is smaller than your network. Then make an IP reservation for IP addresses from outside of your DHCP...

@Hobbit76 The Fritzbox does not require a /24 network. It's just supposed to be a transfer network. She only has one device, the router. A /30 network without DHCP should also be enough, but I also...

@Hobbit76 The 7590 is now configured with the 192.168.0.1/29 network. Why /29 why not /24 ? What's its DHCP server range set to ? How is the WAN port of the ER605 configured ?