The following steps will help you create and configure Google app that the API will use to configure your GTM container. This is a recommended approach for security-savy customers. If anything is unclear, please contact our Helpdesk, support engineers will be happy to clarify stuff for you.
Go to Google Developer Console
Click Projects dropdown (top left corner, next to Google APIs logo), then click NEW PROJECT from the popup
Name your project e.g. My GTM and click Create
On the next screen, click ENABLE APIS AND SERVICES (Make sure that the Projects dropdown is set to your own project e.g. My GTM)
In the API library, type "Tag manager" and once found, click Tag Manager API and click Enable
Click Credentials on next screen
On Credentials menu click CREATE CREDENTRIALS and select oAuth client ID
Click Configure consent screen
Enter application name, can be custom text
Upload your own logo (optional)
Under Authorized domains enter: anowave.com
Under Application Homepage link enter: https://www.anowave.com
Under Application Privacy Policy link enter: https://www.anowave.com/privacy-policy/
Under Application Terms of Service link enter: https://www.anowave.com/product-support-policy/
Click Save
On next screen, set Application type to: Web application
Give your app a name
Under Authorised redirect URIs enter: https://oauth.anowave.com/ (enter exactly with the end slash)
You will be presented with client id and client secret, save or copy them.
Enter your client id in the input below
Enter your client secret in the input below
Save config, clear cache and logout from Magento
Login again and Sign in to Google from the module