Solid Magenta on brand new 753 router

Hi there, pretty frustrated at the moment. I replaced my working, but struggling BT Whole Home Wi-Fi mesh with the RBK753 and can’t get it to connect to the internet - the router just shows a solid magenta light - the 2 satellites seem ok. The app shows the router to be ‘offline’ but doesn’t give any guidance of what to do to resolve this. S

I’ve re-run set up a few times, deleted and reinstalled the app, pressed reset to restore factory settings and finally given up and gone back to my old BT mesh set up. I also continued to use the same Orbi- supplied cable when re-connecting the BT system - I’m now back online.

So I know it’s not the cable, it’s not the ISP provided router/modem on which I have the Wi-Fi signal switched off, it’s not the supply of a decent signal into my home because the BT system is now back up and running fine

It’s probably worth noting that when setting up the Orbi router the app at first couldn’t find it after 3 attempts but then randomly sorted itself out. But proceeding through the rest of the set up process, I got to the firmware update page and it just won’t update - I’ve tried about 5 or more times and each time it fails.

Any advice to resolve this will be much appreciated