The Era-300 needs a dongle to use Line-In.  See here:

https://www.sonos.com/en-us/shop/sonos-line-in-adapter

@jgatie yes thank you. I did buy that as well.  Its all being delivered this week.  I just wasnt sure about what input on the receiver I should connect to.

ive seen in other threads to connect to the tape spot on receiver.

Remember you need an output, not an input.

thanks @106rallye I think when I get home from work I will post a photo of the back of the receiver and that will help other members to direct me.  Very difficult with nothing to reference.

For your purposes, the ERA 300 is a tape recorder. In vintage gear this connection is usually labeled as “REC OUT” or “TAPE OUT”. On the receiver you would select “Phono” as the source and the turntable would be routed to REC OUT.

Thanks @buzz here is a photo of the back of the unit. It has both rec and tape out. I suppose I can just test a couple hookups

In this case “TAPE” is an input for tape playback. You want to use “REC OUT”.

@buzz thank you so much! This is awesome. So glad to have found this forum. Really looking forward to getting my records playing again. This is such a nice receiver too. I think it will sound great. 

@buzz thanks again for the help. One more question to clarify. I connect the era 300 to Rec out and the record player to phone in right? Here is a photo of the front of the unit. 
 

Assuming that this is a vintage turntable without a built-in preamp, it should be connected to “PHONO 1” in the rear. If present, be sure to connect the turntable ground wire.

Sweet @buzz thanks again. I’m doing it now. Hopefully the Ramones will be blasting soon!

Thanks @buzz everything is working. None of the “effects” like base treble volume etc on the receiver make any difference to the playback though. Perhaps that’s just the way the setup is. The volume doesn’t even do anything on the receiver. 

This is the way that it should operate. If you want these controls to be active, move the connection to PORT to “PREAMP OUTPUT”, but I don’t think that you or other operators will appreciate the resulting “war” between SONOS and receiver controls.

Ok thanks @buzz i couldn’t have done it without you. I’ll give it a try and see what happens. I’ll leave you alone for now. 

I messed up and chose the wrong the best answer and don’t know how to resolve. Just to be clear it was @buzz who had the best answer. Very helpful. Thanks as well to the others that responded. I have everything wired up and working perfectly. Sounds amazing as well.