I have just had a very quick look at your code. It seems very long and complex. For initial testing I suggest you try something very much simpler that just sends "Hello World" repeatedly.
I had missed the fact that the other end of your link is on an RPi and I don't have one of them. I would be curious to see a simple example of nRF24 code for an RPi.
There is a simple two-way system in the pair of programs in this link. It should not be difficult to adapt one of them to work on an RPi. If you choose to try that make sure only to make changes to one of the programs.
It would also be good if you have a second Arduino so you could prove that the system works before trying to adapt it to the RPi.
...R