slash_command_button-clicked.py

import json
from urllib import parse as urlparse
import urllib.parse

def lambda_handler(event, context):

    request_body = event["body"]
    decodedBody = event["body"].replace('payload=','', 1)
    decodedBody = urllib.parse.unquote(decodedBody)
    decodedBody = json.loads(decodedBody.replace("\\",""))

    returned_text = "*Request received from Slack button click:*\n" + str(event) + "\n\n*Request body _before_ decoding:*\n" + request_body + "\n\n*Request body _after_ decoding:*\n" + str(decodedBody) 
    return {
        'statusCode': 200,
        'body': returned_text
    }