The Play 1 and the One are NOT the same model speakers.

Have a look here:

https://support.sonos.com/en-us/article/create-a-stereo-pair

Can you post a picture of both speakers? 

If they are the same speaker and you are using the new app, try connecting the speaker you recently purchased to your router/network with a cable and check for updates. The new purchase may be on a different firmware version.

Never said anything about Sonos One. I do have a pair of them and they work great together 

​@Errol66 

Are both Play 1s on the same software? Have you checked for software updates? Possibly they are on different software which is preventing them pairing?

Edit- ​@Pools-3015 already said this, sorry….

Moderator edit: removed picture with serial numbers

There is no problem doing anything with them individually. Updates etc. When trying to pair it acts like they are two different models 

​@Errol66 

They may work individually but have you checked for software/firmware updates though?

Updates on both were not a problem 

This is certainly odd, I’d agree. They’re both PLAY:1s, they should stereo pair without issue. Although there are some Sonos soundbars that they can’t be used as surrounds for. I’d be tempted to power cycle them as a another attempt.
 

Have you called Sonos Support directly to discuss it?

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

Have you got them both in the same system, or did you create a new system when you added the new one?

Can you group them? 

That says the system can’t see another Play:1 so it can’t create a stereo pair. 
 

So, I’ll ask again:

1/ Have you got them both in the same system, or did you create a new system when you added the new one?

2/ Can you group them? 

I have repeated all my processes over again and again, I now have pairing. Conclusion? Can not explain. Much appreciation to all those you contributed to solving the issue