How can I troubleshoot my AWS Lambda function?

I created a lambda function in AWS and apparently it is throwing an error. Here it is:

import json
from urllib.error import HTTPError, URLError
from urllib.request import Request, urlopen
import boto3
#Create a SSM Client to access parameter store
ssm = boto3.client('ssm')

def lambda_handler(event, context):
    # TODO implement
    #return {
    #    'statusCode': 200,
    #    'body': json.dumps('Hello from Lambda!')
    #}
    
    slack_message = {
        'text' = f'Hello World'
    }
    
    #retrieve webhook url from parameter store
    webhook_url = ssm.get_parameter(Name='slackwebhookurl', WithDecryption=True)
    
    #make  request to the API
    
    req = Request(webhook_url['Parameter']['Value'],
                    json.dumps(slack_message).encode('utf-8'))
                    
    try:
        response = urlopen(req)
        response.read()
        print("Messge posted to Slack")
    except HTTPError as e:
        print(f'Request failed: {e.code} {e.reason})
    except URLError as e:
        print(f'Server Connection failed:  {e.reason})

It's triggered by an AWS SNS notification. It's supposed to grab a webhook url for a slack channel and then send the notification to Slack.

Can anyone see what the problem is?

If it's not obvious, can someone direct me to a tutorial on how to test AWS Lambda functions?

Thanks.