Log In confusion

Lora Gateway noob here :
Installed a Rak 2245 PiHat and flashed a 128G SD with chirpstack-gateway-os-full-raspberrypi-20200910132714.rootfs.wic.gz image.

After booting I get a terminal prompt for raspberrypi3 login. None of the creds I provide let me login.
I tried ChirpStackAP, admin, default pi uid and pw.

Can’t get past this, please advise.

read the docs here