Did you select the ‘more options’ link? See this Sonos support document:

https://support.sonos.com/s/article/5097

Sorry, I perhaps should have been a little more specific…

If you reset the S2 App first, then try via the ‘more options’ link as described in the support document. If that works for you, then add the Play:5 (gen2) speaker to the S1 App and if you still need the S2 App after that process is complete, then simply reconnect the S2 App back to the ‘existing’ S2 system… it’s easier to switch off any S1 system devices whilst you complete that reconnection. 

Hi Ken_Griffiths - thanks for the reply.

I’m trying to downgrade my Play:5 from S2 to S1. The steps tell you to factory reset the Play:5 (done), then go into S2 to downgrade. When I go into the S2 app (which I’ve reset) and go to more options and select downgrade, it then searches for devices. It never finds my Play:5. This is the issue I’m having.

@happyshopper885,
I was just thinking the other method outlined, via ‘more options’ might have perhaps worked for you.

Anyhow, have you tried rebooting the network router, aswell as your speaker & mobile controller device?

Does the mobile device and local network meet the system & app requirements, as mentioned in these two links below:

System:

https://support.sonos.com/s/article/126

(note the 802.11b/g Wi-Fi modes and Open, WEP, and WPA/WPA2 Personal Wi-Fi security standards)

S1/S2 Mobile App:

https://support.sonos.com/s/article/4875

If all has been tried and the requirements are met, then it’s probably best you contact Sonos Support Staff (when available) via this link below:

https://support.sonos.com/s/contact

If you do find a solution, please kindly post that back here, as it is a new S2-S1 downgrade method and it would be useful to know the cause of the issue and the eventual outcome.  

Yeah, I’m way past these. I have an iphone12 and have been using S2 and S1 for a while now no problems. Then I learned I could downgrade the play:5 from S2 to S1 and wanted to do this but it doesn’t work. It’s really annoying.

I don’t see why it doesn’t let you downgrade that speaker, I’ve never read anything to say a Play:5 (gen2) won’t transition from S2 to S1. Maybe chat to Sonos Support and let us know what you discover. 

Really appreciate your help. I’m just going to give up. I’ve lost so much time on the S1 vs S2 shenanigans I can’t face Sonos chat.

It might be too late for others, but I found that finding a product to downgrade required first that I install the S2 app fresh, and ensure it is connected to the same wifi network as the product to be downgraded. This might require you to connect to an existing network, then when the prompt to upgrade the software appears (because it wants to re-add the product you want to downgrade!) don’t hit ‘Continue’ (because that will upgrade the product) but instead force-stop the app from the phone’s Settings - Apps options.

I also found that to downgrade more than one product I had to force stop and restart the app each time, otherwise it just saw the previous product and not others.

Also a good idea to power down the downgraded products so that the S2 app doesn't try to upgrade the product back again and send you back to square one.

I had to do this multiple times after a teen upgraded the system (which I don’t want to do because of a connect:amp that is not upgradeable) to S2. Took me all morning and into the afternoon with repeated logins to our account and to the wifi (always painful on a mobile device keypad). Should be made much more straightforward to do this.

I bought a Sonos One and had to go through the rigmarole of downgrading. Not a nice experience!.

Cannot downgrade oneSL. That means it is incompatible with other Sonos products. Very bad experience. I will never recommend Sonos again. 

There where valid reasons for the S1/S2 split. Why is this a surprise for you? Sonos does publicise this: https://support.sonos.com/s/article/5097?language=en_US

The One ís downgradable.

But the OneSL isn't.

I believe it runs fine in an S1 system but once upgraded/added to S2 it can't go back.

That's a bit poor if the One SL can run on S1 but not be downgraded if it is "upgraded" to S2..

Happy to be corrected on that - and also interested in the reason why it's the case (if indeed it is).

I have just purchased a couple of One SL's to add to my my existing S1 system. I currently have Connect's, Connect AMP's and a CR200 Controller. All S1 series devices only.

The S1 app sees the One SL and tells me it needs downgrading. I follow all the instructions, install the S2 app and go through the downgrade process... but alas it cannot discover it to downgrade.

Both the S1 and S2 app can discover it normally.

The retailer believed it could be downgraded and the online documentation appears to indicate it should.

The notes on this article imply that they are initially compatible with S1…

https://support.sonos.com/s/article/4786?language=en_US

1 One SL can only be added to S2 systems. One SLs that are already part of an S1 system will continue to work as they do today.

But no success, so back to the retailer i go.

It looks like I'll have go upgrade from One SL's to straight One's with Alexa which I don't want/need.

Yes, once an old Sonos One-SL (pre-May 2021) has been allocated to an S2 system, there is no going back. They cannot be downgraded to S1. It’s also the case that any new purchased One-SL’s (post May 2021) are S2 compatible only.

i know this  thread is a little bit old but this is what i did.

i purchased a play 5 gen 2 from offerup. i tried just resetting and downgrading but that didnt work.

1. i had to add it to my sonos s2 app, (it then did a firmware upgrade).
   2. i did a reset s2 app
   3. i did a reset of the play 5(holding down the sync button while plugging in).
   4. opened up the s2 app and ran through the “other options” to do the downgrade and then it worked.

hope this helps the original poster if he still is having issues.