Webhook requests being sent as GET requests to Rails server

I'm having trouble getting the payload for the hooks. The requests come through as GETs to my Rails app:

#!ruby

method=GET path=/commit_comments format=*/* controller=commit_comments action=create status=200

Why are the requests being sent as GET instead of POST? I cannot find the payload anywhere in the raw request. Has anyone been able to get the webhook payload from a Rails app? My routes are pretty simple:

#!ruby

match 'commit_comments', to: 'commit_comments#create', via: [:get, :post]

I am trying both get and post to match the Python example code.