I have B-L475E-IOT01 and follow the ppt to connect to AWS IOT. But it cannot connect to AWS, the error message below. The firmware inside B-L-475E-IOT1 is original, come from the board, I do not flash any new firmware.

[kli.7]

*** AWS connectivity demonstration ***

AWS IoT SDK Version 2.1.1-

MQTT connection in progress...

 Attempt 1/3

ERROR: iot_tls_connect L#301 failed

 ! mbedtls_ssl_handshake returned -0x7780

 Attempt 2/3

ERROR: iot_tls_connect L#301 failed

 ! mbedtls_ssl_handshake returned -0x7780

 Attempt 3/3

ERROR: iot_tls_connect L#301 failed

 ! mbedtls_ssl_handshake returned -0x7780

ERROR: subscribe_publish_sensor_values L#263 Error(-4) connecting to a351b2tqauxa3k-ats.iot.us-west-2.amazonaws.com:8883

Error connecting to Cloud!