[stumped]

i got Bookari to work via one very specific route, which I will now try to describe.
You must not complete checkout in any other app. so do not complete checkout on a PC and clear any default android open with that could jump in when you select download epup from the library loand checkout page.[ clear the open with that your browser is aware of, ans you will be interacting with a web page.

then go to your library in your tablet browser , login with your library card, and borrow book. At Checkout, when you now tap download epub, android should ask with what? and Bookari should be an option. [ Bookari needs to be pre-prepped with your adobe ID ]
I think i gave mine both that and the overdrive one.].
I suspect there are 2 working variations 1. login to library with library card, have ADE in booakari, or 2) login to library with overdrive account, have overdrive credentials in Bookari.
the magic drm removal seems to happen as the book is downloading from the library to the tablet, and so that app that is managing that provess gets a read authorisation.

I really wish there was proper documentation , with flow charts, and an explanation of how the security tokens work.

I have moved on to libby and only libby : checkout in libby , read in libby , try not to complain too much about lack of features....but the above is what worked for me for Bookari, ( google play store version) . logically it should work with Aldiko also but I got cross with Aldiko when it insisted that England, UK does not have any public libraries, and deleted it !
Moon+ is a non starter - it wisely? stays out of the DRM fracas. so that's all my epub readers spoken for
Id be interested to hear of any other candidates though.