Thank you. Please accept my apology, my description is poor; by directing the the Access Point - Extender to Bridge rather than double-NAT, consolidation into one network is the outcome I am looking for help to achieve.
I tried hardcoding the IP address of the client Shelly Pro 1 PM, and lost it. The Access Point - Extender did not want to know about it. Here is a picture describing the one network.
Yes, the Shelly Pro 1 PM client it just out of reach of the normal WiFi, a common scenario for Pro 1 PMs that regularly sit in a metal box which is why Shelly have designed the Access Point and Range Extender function.
For anyone with the same issue; there is no need to try to manipulate the client onto the same WiFi network, bridge mode, scripting or hard-coding; use the Shelly Access Point IP address and port 13756 in the HomeAssistant Shelly integration when you hit the “Add device” button.