How to set up Ultra Hub as Access Point over Ethernet

I am looking for help with setting up an Ultra Hub as an Access Point in an existing cascaded router network.

I am new to Geekzone (with a basic knowledge of networking). Have tried searching the forum but can't find the solution.

Background / Existing Network

We have "minor dwellings" adjacent to our home that are set up as small rental properties / serviced apartments - we provide broadband as part of the package. Typically maximum 14 users; maximum devices could be up to 50, mostly wireless devices, maybe 3 laptops hardwired to ethernet LAN ports.

We have the latest standard Spark Huawei (HG659b) Modem / Router with an excellent fibre connection. (100MBps download at source).

I have standardised on Cisco X3500 routers - hardwired LAN to WAN using Cat5e ethernet cabling.

There are 4 of these Cisco X3500 cascaded routers around the site with two 100MB switches in the network to enable the mix of LAN ethernet desktop connections and wireless devices.

There are 3 long separate cable runs on the network - each around 40 to 60 metres.

With the "lockdown" we have 6 or 7 people working from home as well as maybe 3 or 4 Netflix streamers and probably two or three of the users connected to their company remote VPN's.

I was worried about reaching the limitations of a single fibre connection with our distributed network and multiple cascaded routers with the higher use during lockdown......... However, all works reliably at a typical minimum speed of 80Mbps download speed at the farthest reach of the network when the users are within a few metres of the Cisco WiFi Routers using wireless devices.

So no complaints thus far. :)- All users seem happy.

The Problem

I have two spare Vodafone Ultra Hubs available in good working order. After a bit of fiddling around (and a steep learning curve) I eventually figured out to how to configure this as either a LAN to WAN (DHCP enabled etc) cascaded router or a LAN to LAN (DHCP disabled) on my network.

For the LAN to LAN my laptop (and other devices) connect using WiFi and show as connected to internet with the IP address within the range of the upstream Cisco Router. The Cisco shows them all as connected.

However, the internet does not work.

Can the Ultra Hub be used as a "secondary" cascaded router either LAN to LAN or LAN to WAN hardwired ethernet?

If yes, what setting(s) do I need to change to get the connection through the internet? Maybe a DNS problem, static IP address required or ???

Or maybe Vodafone have a firmware of software block on the Ultra Hubs to prevent re-purposing?

Thank you - I've spent hours on this!

JEM