Cannot sync my iphone to my iTunes

I've downloaded Playbox Hd onto my nonjailbroken iphone 5SE running ios 9.3.5. Ever since, everytime I connect my iphone to my iTunes, I kept repeatedly receiving a message telling that my device cannot be sync'ed to iTunes because my computer is not authorized. I removed the Playbox HD app, restarted my iphone, redownloaded latest version of iTunes and reauthorized my computer. Sadly, nothing changed (the message kept coming back again and again). Please guys help me syncing my iphone to my iTunes.