Visa/MasterCard/Amex already support such a facility in India due to RBI requirements. Doesn't seem too difficult to adapt similar functionality for other countries too, if the regulations are updated to require it.

* https://www.visa.co.in/about-visa/newsroom/press-releases/vi... * https://pgi.billdesk.com/web/sihub

> Deep link would require knowing the cancel page of every sub, plus handling auth factors.

All it needs is a "payment refused, user canceled service" response to billing and not to flag the billing attempt as fraud.

> How would this be tooled? A chargeback, a deep link to the cancel page, an API connection between bank and subscription?

I'd be happy to just have the ability to easily ask the credit card company block further payments with no actual notification to the business besides that the monthly charges stop going through. If you want to be fancy about it, creat a custom industry standard declination reason for that use case.

> an API connection between bank and subscription?

This already exists. Mastercard (and Visa?) has an API that lets banks notify subscriptions when your card changes to update the card number https://developer.mastercard.com/product/automatic-billing-u...

This is another instance where we clearly need a regulator to make things work better for the consumer.

Considering they are placing the charges in the first place, it would seem like it would just need to be a response code, not a convoluted network of extensive new development like you suggest.

Integrations are usually one-way (merchant calls bank API), but it's not beyond the bounds of practicality to keep a handle on whatever UID was assigned to the recurring payment in the first place, then send the merchant "by the way this subscription UID requested user cancellation".