shopify_app gem webhooks not working on Heroku environment

I use the shopify_app gem to add webhooks to my app.
They work as expected in my local environment, but when I use the app from my Heroku environment, nothing happens when I do actions that should trigger the webhooks, nor is there any errors or anything at all in the logs.

Any ideas for how I should proceed to determine what the error is?

Update c.f. Davids comment (thanks for the input David):

I’ve added a call to the API to see which webhooks are installed for the app, and I can see the webhooks have not been succesfully installed – I will dig into this.

My procfile for Heroku has the following content:

web: bundle exec rails s
webpacker: ruby bin/webpack-dev-server
inventoryworker: bundle exec sidekiq -q default -q urgent -c 3
clock: bundle exec clockwork scheduler.rb

The Heroku setup is as follows:

• one dyno for “web bundle exec rails s”
• one dyno for “clock bundle exec clockwork scheduler.rb”
• one dyno for “inventoryworker bundle exec sidekiq -q default -q urgent -c 3”
• one off dyno for “webpacker ruby bin/webpack-dev-server”

I am expecting the webhooks to be handled by inventoryworker?

Thanks,
-Louise