One of the reasons this is not possible are payment processing fees.
Here is Stripe (used by Kagi):
2.9% + 30¢
per successful card charge
+ 0.5% for manually entered cards
+ 1.5% for international cards
+ 1% if currency conversion is required
So if you pay $1, Kagi gets something like $0.65, meaning it just lost 35% on the payment processing fee. There is no way this can be profitable to serve the service.
freeCodeCamp uses UPI for donations, and it is free (so far), and you can pay YouTubers through Super Thanks via UPI. Homegrown solutions like PayU and Razorpay are solid, too.
I have previously donated to fCC and sent Super Thanks via UPI. It's seamless experience.
Now the question is whether it will be worth it to Kagi to maintain all these- I think- yes! Once these are set-up, these are low maintenance and you don't need to babysit it. Setting these up, catching up with local tax laws sound like a big barrier, but it really isn't.
Here is Stripe (used by Kagi):
2.9% + 30¢ per successful card charge + 0.5% for manually entered cards + 1.5% for international cards + 1% if currency conversion is required
So if you pay $1, Kagi gets something like $0.65, meaning it just lost 35% on the payment processing fee. There is no way this can be profitable to serve the service.