This repo showcases how to send a webhook to a Google Hangouts Chat room using Apex and Process Builder.
Read more about it in this blog post.
And don't forget to check out the other repos:
You need to have an active G Suite organization (sign-up here as a Salesforce customer if you don't have one).
The Chat documentation explains in detail how the Webhook implementation works.
Clone the repo to your local file system.
git clone https://github.com/muenzpraeger/salesforce-google-hangouts-chat-apex-webhook
Change into the git repo directory and create a new scratch org.
sfdx force:org:create -a apexWebhook -s -f config/project-scratch-def.json
Push the source to the newly created org.
sfdx force:source:push
Open the scratch org.
sfdx force:org:open
Create a new version of the Google Hangouts Chat Process Builder flow and update it with a webhook URL of one of your Chat rooms.
For licensing see the included license file.