Nikon D780 DSLR Camera (Body Only) - Manual (Page 461)

415 Network Connections
Connecting via Bluetooth
Before connecting via Bluetooth for the first time, you will need
to pair the camera and smart device as described below. The
pairing instructions for Android and iOS differ slightly.
D Before Pairing
Before beginning pairing, enable Bluetooth on the smart device (for
details, see the documentation provided with the device), check that
there is space available on the camera memory card, and ensure that the
batteries in the camera and smart device are fully charged to prevent the
devices turning off unexpectedly.