To my knowledge, there is no 3.5mm line in, it’s a USB line in that requires the Sonos dongle. US link provided for personal ease of effort, check your own ‘store’

There is no built-in Line-In.  The Line-In requires you purchase the above USB-C dongle from Sonos.

yes sure, but to connect to this ...which kind of…?

It’s a standard 3.5 mm stereo mini-plug.  Mini-plug cables are available with a number of terminations on the other end, RCA being the most common to connect turntables, CD players, etc.  

Not sure if this is what we’re getting at here, but 3.5 mm ‘male’ ends will have 1 stripe (mono), 2 strips (stereo), and 3 strips (stereo + mic).   They are all  the same size and should be usable, but obviously, the ‘mic’ stripe can’t be used by the Era speakers.  I would think mono cable would work, but stereo is obviously the better choice and readily available.

yes sure, but to connect to this ...which kind of…?

 

It’s a standard 3.5 mm stereo mini-plug.  Mini-plug cables are available with a number of terminations on the other end, RCA being the most common to connect turntables, CD players, etc.  

 

The rounded side of the Sonos adaptor will fit the connector shown to the right in the picture: that’s the 3,5mm jack.

Many thanks!!