walther PRO said 12 months ago on Push Notifications from Scratch :
hmm - my steps were:

1 bundle add web-push
2 rails c vapid_key = ....
3 EDITOR=code --wait rails credentials:edit (c/p-ing the keys from the rails console)
4 add <head> meta
5 update the service_worker.js to getAttribute("content")

(and I don't believe my Chrome being perhaps 1-2 patch releases behind master is the deal-breaker)