Cannot verify Box webhook signatures

I am having trouble with the verification of Box webhook signatures. I have tried using the Python code provided (https://developer.box.com/reference#signatures) and also the AWS Lambda's box-node-webhook-to-lambda blueprint, but I had no luck with both. For the Python code I did not change anything except converting the signatureKey to bytes (required by the hmac.new() function). For the blue print, I did not change any code. However, I only get a 403 error, implying that signatures do not match.

My question is that is any of the Python code in the website outdated? Also, will running my webhook on AWS Lambda affect anything? (I got my Dropbox webhook to work so I'm doubting this is the cause of the error) Lastly, when the Python code example mentioned "Extract the text of the UTF-8 payload as an array of bytes", does "payload" refer to just the "body" of the incoming webhook, or including other information like "headers" etc?

Thank You.