AWS API Gateway POST from SIM800L returns Error 400

Hi There,

I am running my first demo project on the TTGO Call module which has an ESP32 and SIM800L populated on the same board.

I am trying to get the module to POST data to an API I have created on AWS API gateway. The API is very simple and I have tested that it works correctly using Postman and from the command line using curl.

My code is using the TinyGsm, TinyGsmClient and HttpClient Libs.
The Modem starts ok
APN connection is ok.
Connection to End point is ok.
But the POST always returns the same error.

HTTP/1.1 400 Bad Request
Server: awselb/2.0
Date: Tue, 05 May 2020 12:25:57 GMT
Content-Type: text/html
Content-Length: 236
Connection: close

400 The plain HTTP request was sent to HTTPS port

400 Bad Request

The plain HTTP request was sent to HTTPS port
  1. How do I manually discover which version of firmware is in the SIM800L
  2. How do I manually enable SSL if it is available in the SIM800L I am using?
  3. Any other advice you think might be useful?

Check which form of authentication the AWS API supports and the encryption level required. SIM800L might not support TLS1.2 if AWS needs it.