Had the same issue. From what ive read in the forums is that roku will not let you install the app on altered software like Jailbroken or rooted devices. Ive had the amazon tablet for years now. Its something that I believe is a newer issue now. Why they do this is beyond me, as every other app can be installed via the play store on the Amazon tablet, but because you've altered the devices software, Roku blocks it. Crazy. You can still use the app as a remote and connect to the the device v8a Bluetooth, but you cannot sign in.
Hmm . I have no idea how do any of those things you mentioned lol. I haven't done anything to the fire tablet other than downloading the Google play store and installing a few other apps from there, like Kindle and Hulu
I thought you couldnt download the google play store app on the amazon tablets unless you did alter the software. Also on the app, it doesnt allow for Tablet version for some reason.
Ohhh I see what you mean. Sorry I did not understand. Yes I did install some things to be able to involve the play store, I totally forgot because I watched a video and completely forgot what I did lol. OK that makes sense thank you!