Access to 'client' network from 'server' network with Wireguard

Hi there,
Apologies if I should have been able to find the answer to this - but none of the many things we have tried have worked so far.
We have:
Server. MV1000 connected to internet with port forwarding to give access to Wireguard port. Router @ 192.168.8.1, LAN 192.168.8.0/24

Client1. MV1000 connected to internet. Port forwarding not possible. Router @ 192.168.0.2, LAN 192.168.0.0/24

Client 2. MV1000 connected to internet. Port forwarding not possible. Router @ 192.168.22.1, LAN 192.168.22.0/24

What we would like:
Ability to Wireguard from Client 1 & Client 2. Client 1 & Client 2 machines able to browse Server LAN and Server LAN machines able to browse Client 1 LAN and Client 2 LAN.

What we actually have:
Ability to Wireguard from Client 1 & Client 2. Client 1 & 2 machines are able to successfully browse machines on Server LAN but Server LAN machines are not able to browse Client 1 LAN and Client 2 LAN.
Machine on Client 2 can ping 192.168.0.2 (Client 1 router) but cannot ping 192.168.0.108 - which is another device on the 192.168.0.0/24 network. Same is true from a machine on the Server LAN.

Steps to re-create:
Factory default 2 x MV1000, updated to sv 3.105
Sign up for trial of GoodCloud Site to Site service
Register 3 x devices (or 2 - problem is the same with 2 devices) with Goodcloud service
Create Site to Site network in Goodcloud

We have also created Wireguard tunnel manually through the GUI. Tunnel behaves identically - connects fine, can ping either router from either end and can browse server LAN machines from client end, but cannot browse Client network devices from server end devices.

It all feels agonisingly close - like just there’s one step that we’re missing or isn’t working. If anyone has an idea of what that step might be on these devices on this s.v. I would be hugely grateful for advice.

Very many thanks, Dave