[Python] Can I return just HTML using a Lambda @ Edge?

I'm trying to use Lambda at Edge, and based on the status of the request, to return some HTML. Basically the following is my Lambda code (in Python):

def handler(event, context):
clientIp = event['Records'][0]['cf']['request']['clientIp']
status = event['Records'][0]['cf']['response']['status']
headers = event['Records'][0]['cf']['response']['headers']
response = event['Records'][0]['cf']['response']

html = f"""
<!DOCTYPE html>
<html>
<head><title>Access Denied</title></head>
<body>
<h1>Access Denied</h1>
<p>Your IP address is: {clientIp}</p>
</body>
</html>
"""

if status == '403':
new_response = {
'status': '403',
'statusDescription': 'Forbidden',
'headers': headers,
'body': html,
'bodyEncoding': 'text',
}

return new_response
else:
return response


My cloudfront distribution has an AWS WAF associated with it (that should give the error 403) -- however this doesn't seem to trigger my Lambda at all. When I have the WAF associated with my distribution, it just gives me the standard 403, and when I remove the WAF it just directs forward to my domain -- in both cases my lambda doesn't seem to be triggered, despite the fact I've explicitly attached it to the distribution (using CDK) and explicitly mention the version of the Lambda.

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