In the documentation it says:
To sign up for Google Pay:
Step 1. In the Authorize.Net Merchant Interface https://login.authorize.net, navigate to Account > Settings > Digital Payment Solutions. The available digital payment solutions appear.
Step 2. In the Google Pay section, click Sign Up.
Step 3. Enter your KeySet ID and generate a Signature Key if you haven't yet done so.

But no any information where and how I can get KeySet ID. Can any body help me in this?