Webhook to AWS API Gateway error: {"message":"Forbidden"}

Hi all,
Some basic information on what I want to manage in AWS:

Goal: I have a Particle board. This Particle board is an arduino like board with a GSM modem. This board sents data to the Particle Cloud. In the Particle Cloud I want to use a webhook to send the data to AWS API Gateway. After this a lambda function should insert the received data into a dynamoDB.

What I already did:

• I followed this instruction for the API: https://aws.amazon.com/de/blogs/aws/amazon-api-gateway-build-and-run-scalable-application-backends/
• I created an API Key. I chose that an API Key is required. I'm adding this API Key into my header on the request (using Postman to test the API.)
• deployed the api.
• I'm calling the api like this: https://XXXXXXXXX.execute-api.eu-central-1.amazonaws.com/prod/data

Problem:

• request looks like this (postman):
  GET /prod/data HTTP/1.1
  x-api-key: MY_API_KEY
  User-Agent: PostmanRuntime/7.26.3
  Accept: /
  Postman-Token: 326808aa-a0c0-49fa-952e-bbac3ce2fe97
  Host: XXXXXXXXXX.execute-api.eu-central-1.amazonaws.com
  Accept-Encoding: gzip, deflate, br
  Connection: keep-alive

• response (postman):
  Date: Thu, 13 Aug 2020 15:36:32 GMT
  Content-Type: application/json
  Content-Length: 23
  Connection: keep-alive
  x-amzn-RequestId: 12a821d3-77be-46d5-8889-b03fd98a1942
  x-amzn-ErrorType: ForbiddenException
  x-amz-apigw-id: RNugJGJWliAFlHQ=

{"message":"Forbidden"}

When I'm disabling the need of the API Key the API is working as expected.
I'm not sure which step and/or setting I might have missed.
Does somebody can help me?

EDIT: Here is the Particle Webhook documentation. But I think it's not necessary as Postman also fails. So it is certainly not a webhook error. :)
https://docs.particle.io/reference/device-cloud/webhooks/#sending-complex-data

Best,
Tim

Edited by: T1mS on Aug 13, 2020 8:41 AM

Edited by: T1mS on Aug 13, 2020 8:43 AM

Edited by: T1mS on Aug 13, 2020 8:45 AM

Edited by: T1mS on Aug 13, 2020 8:46 AM