Are you trying to create a webhook record or just generate an access token? You can authenticate with the API by running a local webserver which is explained in the developer dashboard when you add an API gateway.

As previously mentioned, ngrok is the easiest way to create an instant tunnel with https. The issue you'll run into is validating the webhook events. If you're new to Clio and are trying to test the waters, please be sure to delete the webhook subscription when you close the tunnel so resources aren't being wasted sending requests to a server that doesn't exist

If you're trying to create a development environment, an e2-micro instance with a reserved external IP running NGINX costs like $7 a month. We ran an e2-micro VM as a reverse proxy using NGINX and certbot and forwarded the requests to an e2-medium instance which allowed us to work on the code without having to constantly change endpoints and redirect URIs in the API gateway. Create a route in our application with an optional path parameter and when subscribing to a webhook, map to the X-Hook-Secret to the path it was first received on.