There are various way to POST JSON to one of your AWS Lambda Functions.

• POST JSON to a Lambda Function using AWS console Test Event
• POST JSON to a Lambda Function using cURL
• POST JSON to a Lambda Function using EventBridge Scheduler (this article)

Let's say you have a Lambda Function, perhaps something like this (Python in this example). This is just a super simple example with no error handling to highlight the most relevant markup. In this example, the Lambda Function expects the input JSON to pass in the foo and bar keys.

import json

def lambda_handler(event, context):
    print(event)

    json_loads_event_body = json.loads(event['body'])

    foo = json_loads_event_body['foo']
    bar = json_loads_event_body['bar']
       
    return {
        'statusCode': 200,
        'body': json.dumps({
            "result": "success",
            "foo": json_loads_event_body['foo'],
            "bar": json_loads_event_body['bar']
        })
    }       

In this example, here is how you would format the input JSON (payload) in the EventBridge Scheduler.

{
 "body": "{\"foo\":\"Hello\", \"bar\":\"World\"}"
}

Notice also in this example that the Lambda Function includes print(event). This is super helpful when testing/debugging, but you probably wouldn't want to include print(event) after your testing/debugging is done, as this could add a bit of additional cost each time your Lambda Function is called.

If you have print(event), then Cloudwatch > Log groups > /aws/lambda/myapi > yyyy/mm/dd/[$LATEST]abcdefg123456789abdefg123456789 should have something like this. For more details on this, check out my article Amazon Web Services (AWS) - API Gateway Lambda Function and Cloudwatch Logs.

{
   "version":"2.0",
   "routeKey":"POST /postSendgrid",
   "rawPath":"/postSendgrid",
   "rawQueryString":"",
   "headers":{
      "accept":"*/*",
      "content-length":"15",
      "content-type":"application/json",
      "host":"abcdefg.execute-api.us-east-1.amazonaws.com",
      "user-agent":"curl/8.0.1",
      "x-amzn-trace-id":"Root=1-65712b4e-32aaec9937d2924457e3df71",
      "x-forwarded-for":"10.11.12.13",
      "x-forwarded-port":"443",
      "x-forwarded-proto":"https"
   },
   "requestContext":{
      "accountId":"123456789012",
      "apiId":"abcdefg",
      "domainName":"abcdefg.execute-api.us-east-1.amazonaws.com",
      "domainPrefix":"abcdefg",
      "http":{
         "method":"POST",
         "path":"/postSendgrid",
         "protocol":"HTTP/1.1",
         "sourceIp":"10.11.12.13",
         "userAgent":"curl/8.0.1"
      },
      "requestId":"PjO0Ujb2IAMEJ9A=",
      "routeKey":"POST /postSendgrid",
      "stage":"$default",
      "time":"07/Dec/2023:02:17:50 +0000",
      "timeEpoch":1701915470546
   },
   "body":"{\"result\":\"success\", \"foo\":\"Hello\", \"bar\":\"World\"}",
   "isBase64Encoded":false
}