I am located in London, UK and I am playing around with the Transactions API for Actions on Google using sample code found in this repo
However, when I run the sample I get the following message "sorry, I can't take payments in your region"
Do I need to enable test mode or something similar?
Unfortunately Actions on Google Transactions APIs are only currently available in the United States.
https://developers.google.com/actions/policies/general-policies
"Currently, the Transactions API is only available in the United States; apps in other countries cannot implement the API or complete transactions until the API is available there."