ServerFilter won't use prepare function

the function is called but the value send to the server is the initial input value.
https://snippet.webix.com/41a4r13s

Hello,

Server filters work in a different manner. They just reload the data based on the Datatable state (which is returned by the getState method), and it always contains actual filter values.

As a simplest solution, you can block the onBeforeFilter event and load the data by API: Code Snippet

Or, a bit more advanced technique, define a loading proxy to modify request parameters just before it is issued: Code Snippet