Boot Node issue

When I create a bootnode, I am not getting the enode. So I used this link for reference to derive it. However, the below is happening. It seems that the bootnode address is 128 bits whereas it is expecting 256.

Any idea what I'm doing wrong?

bootnode -nodekey boot.key -writeaddress

enode@ip:port

The param -nodekeyhex as to be used instead of -nodekey if you generated a hexadecimal boot key.