I think you would need a plugin to setup a route to process the request, but it would be good for someone else to confirm that.
The ideal solution might be for Ko-fi to provide a donation tracker widget that you could embed as an iframe on Discourse. It looks like Ko-fi provide a widget (iframe) that can be used to accept donations, but I don’t see one that can be used to display progress towards a donation goal: https://help.ko-fi.com/hc/en-us/articles/360018381678-Ko-fi-Donation-Widget.