Ring Video Doorbell 3 cannot connect to TP-Link Deco M4 mesh in Access Point mode

I have recently installed a TP-Link Deco M4 Wifi mesh. It connects to a Sky SR213 Router. The Deco M4 is set to Access Point mode because it is not possible to turn off the DHCP function in the Sky router.  This setup works fine for my Ring Spotlight Cam and Floodlight Cam, but the Video doorbell 3 refuses to connect. It recognises the WiFi signal (which is quite strong) but fails with two white lights flashing on the right and the app gives the error code “P7-04”. I cannot find the meaning of this code anywhere.  The Deco M4 is set to 2.4Ghz only, and has Fast Roaming and Beam Forming turned off. The WiFi SSID is letters only and the password is numbers only — no special characters in either. The odd thing is that if I set the M4 network to Router mode, the Video Doorbell 3 connects normally. The other Ring cameras are happy with either mode. However, this breaks several other things because I end up with two subnets — so that is not an acceptable solution.  I can also connect the Video Doorbell 2 directly to the Sky router if I move it near enough; but I want to use it at a location too far away.  Is there a setting I can use to make the Video Doorbell 3 work with my Deco M4 in Access Point mode, or is it simply incompatible?