Figured it out, has to be done on a Mac

openssl ecparam -name prime256v1 -genkey -noout -out private_key.pem
openssl ec -in key.pem -pubout -text -noout 2> /dev/null | grep "pub:" -A5 | sed 1d | xxd -r -p | base64 | paste -sd "\0" - | tr -d '\n\r ' > publicKey.txt