Multi-Account Spotify - Still booted for single device restriction?

Went through and created the dev app, and got all four of my families accounts permissioned in there. Strung it into HA, and installed Spotcast with the sp_dc and sp_key in secrets. All good, and tested for basic functions. Can get any individual account to play through any speaker. Yay!

What I’d like to do isn’t working though. I really need to have two different accounts, playing different music, on different speakers. The sources show up in the media picker as expected, and play, but when I go to the other speaker and select a different account to play, it kicks the kids speaker off with “Your account in being used…” blah blah.

Why oh why is it doing that? Is there any way to make this work as intended? I’ve read through dozens of posts, the integration configuration guides, and I can’t figure out what could be wrong here. This is incredibly obtuse! Someone else has to know what I need to do. Thanks!

ETA: Could this be due to using the same set of cookies for the Spotify account link in the config? That’s the only thing I can think of but I have no clue if this is even something I can do anything about?