Your Nano code is incorrect. The slave SPI device is selected when it's SlaveSelect goes low. You need to exit setup with SS high.
In your loop, you should set SS low, transfer your data and set SS high again.
Your Nano code is incorrect. The slave SPI device is selected when it's SlaveSelect goes low. You need to exit setup with SS high.
In your loop, you should set SS low, transfer your data and set SS high again.