I ‘believe’ you may need an S1 only compatible device to create a new Sonos S1 system. The Play:3 is both S1 & S2 compatible, but perhaps see the instructions here:

https://support.sonos.com/en-us/article/downgrade-a-sonos-product-to-s1

Some further reading…

https://support.sonos.com/en-us/article/set-up-a-separate-sonos-s1-system

https://support.sonos.com/en-us/article/known-limitations-with-separate-s1-and-s2-sonos-systems

Thanks for your help ... I had to:

(1) add the product in the Sonos app;

(2) update the speaker;

(3) downgrade the speaker;

(4) add the speaker in the Sonos S1 app.

It took 2 days of frustration but I finally got there ..!

I heard there was an update to help downgrade from an s2 app to the s1. When is that happening? 

• Delphinus how did you do this? i’ve tried with my 1 but it keeps shutting me out. 

It wasn't easy, but it worked in the end:

(1) add the product in the Sonos app;

(2) update the speaker;

(3) downgrade the speaker;

(4) add the speaker in the Sonos S1 app.

It took 2 days of frustration but I finally got there ..!