Convert SecKeyRef to PEM data

I am trying to retrieve public key and private key from Mac key chain and convert it into PEM format, which will be used by another process.

I am using the following code snippet to retrieve the private key:

OSStatus status;

        NSMutableDictionary *query = [NSMutableDictionary dictionary];

        [query setObject:(id)kSecClassKey forKey:(id)kSecClass];

        [query setObject:(id)kCFBooleanTrue forKey:(id)kSecReturnRef];

        [query setObject:(id)kSecMatchLimitAll forKey:(id)kSecMatchLimit];

        [query setObject:@"<label> forKey:(id)kSecAttrLabel]
          
      SecKeyRef keyRef = NULL;
    status = SecItemCopyMatching((_bridge CFDictionaryRef)query, (void *)&keyRef);

        if (status != errSecSuccess) {
            CFStringRef errorRef = SecCopyErrorMessageString(status, NULL);
            NSLog(@"%s: %@", FUNCTION, (bridge NSString *)errorRef);
            CFRelease(errorRef);
            return ;

        }

I got a Non-Null SecKeyRef object, and no error. I verified the label previously by printing attributes.

But I cannot use this SecKeyRef for any other operations like getting public key using SecKeyCopyPublicKey, or I cannot convert into openssl format using SecKeyCopyExternalRepresentation or SecItemExport.

For SecKeyCopyExternalRepresentation, I am getting the error that "export not implemented for key" error
And with SecItemExport I am getting -25260 error.

 NSData *data = NULL;
    SecItemImportExportKeyParameters params;
    params.version = SECKEYIMPORTEXPORTPARAMSVERSION;

 
    params.passphrase = CFSTR("<pwd>");

    status = SecItemExport(keyRef, kSecFormatPEMSequence, kSecItemPemArmour, &params,  (__bridge CFDataRef)&data);

Could you please let me know If I am missing some other code causing the issue.