Export an elliptic curve key from iOS to work with OpenSSL

I have a private/public key pair generated and stored inside Secure Enclave.

It is 256-bit elliptic curve key. (The only key type that can be stored in Secure Enclave).

I use SecKeyCreateWithData and SecKeyCopyExternalRepresentation to import/export the public key between iOS devices, and it works.

However, the exported key doesn't seem to work with OpenSSL. Because it always show 'unable to load Key' on this command.

openssl ec -pubin -in public_key_file -text

What's the way to export the key ? So I can use it with OpenSSL.