Canvas bot on Slack not working

[zewen]

Hi, I'm hosting the Bitnami Canvas package on AWS, and am trying to figure out how to integrate Slack with the Canvas site. I've followed the instructions here precisely:
https://community.canvaslms.com/docs/DOC-17720-canvas-slack-app-admin-installation-guide 

But when the confirmation popup appears to enable Slack as a contact method, the Canvas bot in my Slack workspace does not do anything (it's supposed to send me a message with the confirmation code). Why is this?