For security reasons, some changes will soon be introduced to LiveID+ concerning the liveid_servercallback parameter, which can be specified when initiating a process (release 2.87.0-rc1 changelog).
All the details can be found on the official LiveID+ documentation (Integration Server-Side Callback section, liveid_servercallback parameter documentation).

This change is already active in the test environment, the production release will take place in the coming weeks.