help with my project - connecting pi with arduino

[liorillusion]

hello. im very new in all this kind of arduino and pi.
i need help. i have 2 codes who was working on my arduino mega and pi 2
i got new arduino mega and new pi 3 and i gave it to someone to install it.
now the code is up but something with the communication or the sequence is not ok and the code crush
i connect the arduino to the pi like that

PI (8) ---------------> AR(17)
PI(10) <--------------------- AR(16)

and i did ssh if you can help me in private and solve the problem, its will help me a lot. thank you very very much!