In Sonos speak "pairing” means setting them up as a stereo pair. The process to ad speakers as surrounds is called "bonding". See Add surround speakers to a Sonos home theater | Sonos

If the two Era's are indeed paired as a stereo pair, you need to unpair them first befor adding them as surrounds to the soundbar.

Thank you so much for getting back to me, how do I unpair please (have tried!)

Here:

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

Thanks I’ve somehow managed to stereo pair them in separate rooms, I’ve tried resetting the app but end up with two rooms with Ray in one and Era in the other think when open App again. I think need to reset completely and start from scratch if that’s possible?

I bought Ray first then got Era so didn’t set up as Surround from scratch….

tyi

Tap the “Settings” icon (far right one of the 5 at the bottom of the screen), then select System, then the room with the paired Eras. Tap Remove Stereo Pair. 
 

Then follow the instructions above to add surrounds. 

Hi, have added 2 era 100’s to my Ray and Sub and went through the whole process and even had the “successfully added” screen on the new App. But when i go back to app screen ( a few hours later to allow for sync), it still shows them as separate. Any ideas how to fix? Not sure if this is because of the new App update or something else?

App update says it’s fixed “issue adding surrounds..”. Rebooted Era’s and added speakers again as different rooms, then tried to add surrounds and got a successfully added but same problem still. Does not show as added to the room which it was added as surrounds