Adding Donation Option to shopping cart checkout on Non-Profit event commerce website

Site URL: https://www.newcanaanrotarylobsterfest.org/

When using the shopping cart on a commerce site for a nonprofit event, how can I add options for the customer on checkout?

• Want to add a line for an optional donation
• Want to add a line for an optional 3% transaction fee recovery fee

There aren’t any built-in options to achieve either of these. A developer could add the optional donation in fixed amounts, but the percentage transaction recovery fee isn’t possible on Squarespace, even with code.