This appears to have been misinterpreted
Pinboard do not use IFTTT but instead IFTTT link Pinboard to other things.
Pinboard already have an API that IFTTT use but IFTTT want Pinboard to implement a private API that IFTTT will use and IFTTT want Pinboard to do this for free.
IFTTT are the ones that are breaking their integration with Pinboard by turning of integration with the current API.
This is the writeup by the Pinboard CEO
https://blog.pinboard.in/2016/03/my_heroic_and_lazy_stand_against_ifttt/