Okay, so I'm new to sideloading, but, I used this website to convert apk to bar. So I tried sideloading a new Kairosoft app on my Playbook; Kairobotica (I paid for it on my Android, I just want it on my PB now) So everytime I download it and sideload it I get:
Error. Authentication failed. Please use the account you used to purchase the app and check your signal.
When I start up the app
Then I pressed OK. It takes me to this page but I don't think these things apply to me, since I'm not on a android. From some webpages I viewed, this app has a "License Verification"
Is it piracy if he paid for the app? He can't use it at the same time on both devices so that would not be piracy or is it?
Depends on the terms, but probably not allow on more then one device. For example OEM applications installed on the brand new <insert PC manufacturer> as licensed strictly to that machine. Now if you bought for example MS Office Home and Student (retail), I believe it can be activated on 3 machines (could be wrong on that).
It might be trying to use some form of Android verification that isn't supported in the PB's Android Player. Have you tried contacting the developer of the app?