Error code 88 trying to configure a Home Assistant MQTT server

Device Nuki Lock 4.0 Pro
Device version: 4.2.8

I am trying to configure the MQTT server but I keep getting Error Code 88:

The IP of my MQTT server and of Home Asisstant is (subnet mask 16)

What I have tried without success:

  • Put the Nuki on my other WiFi network (network an other WiFi AP.
  • Change the username and password to be only letters and 8 characters long.
  • Reinstall Mosquitto Broker Add On

I can connect without problems from the MQTT Explorer client:

According to the MQTT API only private IP ranges are allowed. 192.1.x.x is not a private range.

This was recently asked here too: Smart Lock 3.10.x Beta - #15 by Juergen

Why is there this limitation? Are there security implications I should be aware of if I alias one of my server IPs or is it simply a decision to follow the standard?

After configuring an alias on my router everything seems to be working fine.