Hello Miles,

We would like the customer to be able to opt-in to adding a donation at the checkout stage. The choices would be no donation, £1, £5, etc.

This will need customization. You can take a look at this page https://www.sellacious.com/customization or email us at contact@sellacious.com

One (maybe clunky) way of doing this would be to re-name a choice of shipping function to allow for 'free shipping' or 'no donation' or a donation of value in which would be added onto the total and charged to the customer.

You can change the shipping rules or language name from sellacious backend > Languages > Translations.

https://www.sellacious.com/community-support/3216-changing-field-labels-in-checkout-or-adding-additional-attribute#reply-3231

Thank You