You aren’t doing anything wrong. It’s most likely the new POS app.
 

If you have the desktop app, try start adding the boost on your phone then switch over to desktop ( have the app open on your computer before you start to add it) and see if you get a prompt there. Hope that makes sense 
 

 This worked for people who couldn’t add new speakers so might for your boost but this is just a long shot guess. 

Hi Bumper

Thanks for the quick reply. I tried your suggestion and absolutely nothing happened on the PC Sonos app. And it was open as I used my Android phone Sonos app to try and reads the Boost.

I assume you do not have any of the newer speakers such as Era or Move.
If your speakers connect fine to your new network without the Boost, you can leave it out. I believe other users have done the same without connection issues. If you do have connection issues with a distant speaker, try connecting one speaker close to a node with Ethernet to use Sonos net and extend your coverage.

When you started building your SONOS system WiFi struggled to support multiple players. BOOST worked around these shortcomings by building a private wireless network, ignoring poorly performing WiFi. Current WiFi is much more capable, actually more capable than BOOST. There are a couple issues with the current SONOS software, sometimes defeating BOOST.

Bottom line: Power down BOOST. If the system continues to function, recycle BOOST. 

Hi Pools and Buzz

Great advice thank you. All speakers inc. Move are working without Boost, so I will follow both your advice and dump it. It's just disappointing that it won't work and that Sonos have not adjusted it's firmware to cope.....and or told their clients to forget about it when they have a decent Mesh system. No worries and thanks

Same here great advice… boost seemed to disrupt my whole system. I have been struggling with this for months now. I took the power down and immediately I can play music again. Some terrible customer support from Sonos…Thanks buzz!!!!!