I am simply trying to publish to an SNS topic using a lambda function. The function code as follows, with ARN being the actual SNS topic ARN:

import boto3
print('Loading function')

def lambda_handler(event, context):
    client = boto3.client('sns')
    response = client.publish(
        TargetArn='ARN',   
        Message="Test",   
    )
    return response

The function execution role as access to SNS. In fact I even gave SNS full access. But I keep getting the error:

{
  "errorMessage": "An error occurred (InternalFailure) when calling the Publish operation (reached max retries: 4): Unknown",
  "errorType": "ClientError",
  "stackTrace": [
    "  File \"/var/task/lambda_function.py\", line 6, in lambda_handler\n    response = client.publish(\n",
    "  File \"/var/runtime/botocore/client.py\", line 316, in _api_call\n    return self._make_api_call(operation_name, kwargs)\n",
    "  File \"/var/runtime/botocore/client.py\", line 626, in _make_api_call\n    raise error_class(parsed_response, operation_name)\n"
  ]
}

I do not find any access denied errors in cloudtrail either. Any idea on what is the issue here ?

Edit: Its my bad, I used the subscription ARN instead of the topic ARN causing this issue.