Hi, so with the Google DNS provider we have uses a script provided by the Posh-ACME project, and the main part of using that is that you need to setup a service account and give it access to perform the DNS changes, then download a json key file which you then point to.
The instructions for the Google Cloud Posh-ACME provider are here: https://github.com/rmbolger/Posh-ACME/blob/master/Posh-ACME/DnsPlugins/GCloud-Readme.md and everything up to ‘Using the Plugin’ is relevant. Unfortunately google doesn’t provide any other information when a request fails, other than it’s clear the credentials you are using don’t have enough permission.