A user reported the Site Search report is not available in the mobile app and I noticed the report is not included in API.getReportMetadata.
The reason for this is a check for the idSite parameter: https://github.com/piwik/piwik/blob/master/plugins/Actions/Actions.php#L503
It should work without the idSite parameter as well.
In 2da1fc778d101d2044d1fd843d18eff7eaa88f7a: fixes #4869 site search was not included in report metadata
In f3a53e2536e41f1c9ab70e50b62893715a7e6ea8: refs #4869 fix tests