Unraid does not come with the xxd command installed. There used to be a package called NerdTools that I used to use but it looks like it was removed. I do not recall if you can use docker run in Unraid, but these commands can be used. A quick google indicates windows users can use the docker cli.
# on host
docker run --rm -it alpine:latest sh
# in container
apk add xxd openssl
# everything after this is one command
echo PDS_PLC_ROTATION_KEY_K256_PRIVATE_KEY_HEX: $(openssl ecparam --name secp256k1 --genkey --noout --outform DER | tail -c +8 | head -c 32 | xxd --plain --cols 32)