Setup UTM 9 Home Edition advise

Question

Hi all, 
 I have a fanless mini PC running UTM 9.6 
 In my Home enviroment, I want to use this behind my router, current basic setup shown below 
 
 The new setup should be something like this: 
 
 The UTM was installed with the basic settings, so no tweaking is done yet. 
 When setting my network up as shown in the second picture I could not connect to the internet from behind the UTM, internal connection is no issue. 
 When connecting a device to the Router, I had, of course, internet connection but could not connect to anything behind the devices. 
 So my question, what i'm doing wrong or where should I look. 
 
 thankx and have a happy new year!

Argo · Accepted Answer

Looks like your subnets are having an issue, bit of a conflict going on there. 
 I would first use two separate subnets, say 192.168.1.0 & 192.168.2.0. 
 but having this sort of configuration may involve double natting, which can be a pain to manage and maintain.