I've been looking at all the threads on this topic, but nothing quite fits.
On the checkout page, I want customers to see a button to add a donation to our nonprofit, and then they can enter any amount to add as a donation.
This could work as a donation "product" with a variable price but only if I am allowed to add that product to the checkout page.
The "tipping" feature seems to only use percentages.
Are there any solutions to this?
You can create a campaign so that customers have the option to give a custom amount to your nonprofit (and your store could optionally match it). This will appear on a page after they completed their order, but before the order confirmation page -- through Shopify's new post purchase flow. All campaigns can be configured with just a few clicks, and require zero code.
I am the co-founder of Change, and am happy to answer any questions!