Try a manual update. Try these hints https://support.sonos.com/s/article/2382?language=en_US which includes manual update I mentioned.

Cheers!

Error code 803 is not included in that list.  I’m having the same issue with my (new to me) Play 5 Gen 1.

That’s true error 803 is not listed. In my post l meant that you should try a manual update. The link was for further reference.

I ended up messaging support on Twitter. They had me run a diagnostic, then sent me a unique link to change some setting and force the update. Fixed my issue.

I bought a used connect online and was triggering the error code upon setup. I was able to fix the issue by unplugging all units except for the new (to me) Connect that would trigger the error. With that being the only unit on the system, the update went thru. Then plugged back in  all the other units including a sub, playbar, 3 Play 5’s, 10 play 1’s and 2 more connects. System works as should now. Hope this helps. 

More to the point, the link will not tell you how to perform a manual update.

Correct, it requires a specific update for your individual device/software rev. There isn’t a generic manual update. 

Gnudog got it right.  Start your system, connect your new unit, take everything else off the system, and it will update the new unit.  You still may have to try a couple of times to get the new unit to connect, but from there the system takes over.

I had the same problem adding a Sonos 5. App told me Sonos 5 needs an update. When I ran the update I got the failed notice. More info showed error 803.

I fixed it by turning all the other Sonos devices off and did the update again. This seemed to work for me. I then turned all the others back on and so far so good.

Hope that helps.

Ben