AWS MQTT private key form PEM to DER

Hi,
I followed this post https://forums.openmv.io/t/mqtt-connection-to-aws-iot-core/1464
to connect to AWS MQTT.
I understand that the keys and cert must be binary (DER) instead of PEM
I have manage to convert the cert in DER with openssl but failed to convert the private key form PEM to DER
I’m using the following openssl command
openssl x509 -outform der -in *****-certificate.pem.crt -out *******-certificate.der
for the cert and

openssl x509 -outform der -in *********-private.pem.key -out ********-private.key.der
for the key.
Openssl sprit out the following error message for the key
Expecting: TRUSTED CERTIFICATE
Does any one manage to convert the private key from pem to der?

My micropyhton code to connect mqtt through TLS is:

KEY_PATH = "6336c81ec8-public.pem.key"
CERT_PATH = "6336c81ec8-certificate.der"
with open(KEY_PATH, 'r') as f:
    key1 = f.read()
with open(CERT_PATH, 'r') as f:
    cert1 = f.read()
client = MQTTClient(client_id="esp32",
                    server="aeyd89uk69eiz-ats.iot.us-east-2.amazonaws.com",
                    port=8883,
                    keepalive=4000,
                    ssl=True,
                    ssl_params={ "key":key1, "cert":cert1, "server_side":False })
client.connect()
print ("MQTT client conencted")

OUPS!!!
My mistake…
It finally work with openssl and i succesfully connect to AWS MQTT
The openssl syntax to convert the private key from PEM to DER is:
openssl pkcs8 -topk8 -nocrypt -in <YOURPEMPRIVATEKEY> -inform PEM -out <YOURDERPRIVATEKEY> -outform DER