We're using the out of the box Shopify tip functionality that appears on the Payment page, during the checkout process. You set it up under Settings > Checkout > Show tipping options at checkout.
The issue we're having is the default selection is set to none. We'd like to change that to one of the options with an actual amount, so the delivery guy has a better chance of earning a tip.
Any pointers would be appreciated whether in settings or code!