Got it working. Couple things to note, hope it may help.
Make sure you export the mp3 via amazons standards: https://developer.amazon.com/en-US/docs/alexa/custom-skills/speech-synthesis-markup-language-ssml-reference.html#h3_converting_mp3
Make sure the mp3 is LESS THAN 240 seconds per Amazons rules:
Make sure after you create the skill in your web browser than you open up your alexa app and enable it
Test the skill first with just speech to verify you got that much working, before trying to play mp3. Change the lambda.py to something like the following:
If hosting the mp3 on your homeassistant device, make sure you can access the URL in just a web browser. If it doesnt play in web browser, its not gonna play through your echo
