I hope to follow up on this soon. The method we use to integrate with Libby was undocumented and I expect we’ll have to keep updating it when it breaks.
I’ve been unable to switch to the new Libby setup flow, so instead I’ve fixed Micro.blog so that it works with the “other apps” option in Libby. If you choose Sonos or Android Auto, that code will work in Micro.blog now too.
I fixed some other sync issues too so it should be more reliable going forward.