This is an example project showing how to handle interactivity from slack. It uses Slack Block Kit to add a button to a message and Slack app interactivity to receive a webhook and post a message back to the user.
You'll need to install ruby 2.6.5 and bundler on your machine. I use rbenv which isn't entirely terrible.
$ rbenv install 2.6.5
$ gem install bundler
Then, install the gems in Gemfile
$ bundle install
Finally, you're ready to start the test server
$ bundle exec ./server.rb
Modify server.rb and change the SLACK_URL to your applcation's webhook url.
In this example I use localhost.run to expose my local development instance to the internet to that Slack can invoke my app under development. You may have to do some fancy footwork to install ssh if you're running on a windows box:
$ ssh -R 80:localhost:4567 ssh.localhost.run
Connect to http://xxxxx.localhost.run or https://xxxxx.localhost.run
Make note of your localhost.run https url, it'll change every time you start a new tunnel.
Set the Request URL for your app (as described here) to the localhost.run https URL above with /slack-webhook appended. For example, if your localhost.run https URL is https://awesome-123.localhost.run you'll set RequestURL to https://awesome-123.localhost.run/slack-webhook.
Finally, test it out:
$ curl -X POST -d '{"name": "Gregg"}' -H 'Content-Type: application/json' http://localhost:4567/hello