why cant i download an app after i factory reset it

[AC Question]

I got a my dad's old phone and I used it . I downloaded everything without reseting it and it started acting funny . so I reset my phone and saved all my pics to snap chat and once my phone got done reseting it would let me download snapchat . it says your phone Is not compatible with this app . how do I fix this

 

[B. Diddy]

Welcome to Android Central! Which phone? What version of Android? Are you trying to install from Google Play Store?