Web API Server
Starting in the 8.5 release, Web API Server has its own separate documentation.
The most recent release of Web API Server prior to 8.5.0 is 8.1.2. You can also use that release with eServices 8.5, but note that Web API Server 8.1.2 does not work with Stat Server 8.1.1 and above. More information about Web API Server 8.1.x can be found in the 8.1 version of the eServices Deployment Guide.