Set Data rate on NRF24l01

Hello,
I am trying to set data rate for nrf24l01, but I don't know how(for 250kbps). These are the instructions for the libraries RF24: RF24 Class Reference . I don;t know how to write the codeline and where in code. In void setup?

setDataRate(RF24_250KBPS); will only work on plus units. From the library reference "setting RF24_250KBPS will fail for non-plus units"

I made the setting, but it does not improve the distance. I read that modifying the payload improve the distance. So I set the payload from 32(default) to 8, but now the transmission does not work. Before, it transmitted a "111", and now I can't see anything in receiver. Why does not work with payload set to 8. And what is this payload. What represents? Thank you!

The payload is the data you want to send or receive. I think that, unless you are using dynamic payloads, the payload size must be set to the same value in both ends.

It was set to 8 in both devices. If the payload is set to 8 means that I cand send maximum a string of 8 characters?

I think so. It has been a while since I messed with the rf24.