Works great with the Tea Commerce Starter Kit!
Zero Cost Payment makes it easy for you to use a specific payment method on orders that cost nothing. If you have a discount code or giftcard that results in the orders price being 0, then you can change the payment method to prevent the customer from using a payment provider that requires credit card information etc.
The package installs a simple Razor file and a config file.
You can change the automatically selected payment method in the ZeroCostPayment.config file.
Just change to the desired method id.
<zeroCostPayment storeId="1" methodId="2" />