With the release of FileMaker Server 17, many settings we took for granted were removed from the admin console and require setup from within the command line interface (CLI) or Mac Terminal.
Although documented in the official help system, a while back we were caught out by the following.
To enable the FileMaker API for PHP, use the CLI command:
fmsadmin set cwpconfig enablephp=true
To enable the FileMaker API for XML, use the CLI command:
fmsadmin set cwpconfig enablexml=true
The above must be enabled on the 'master' machine in a multi-server setup.