Signatures for the “onBeforeAjax” event do not match.
ajax
callEvent(“onBeforeAjax”, [mode, url, params, x, headers, null, defer])
Uploader
callEvent(“onBeforeAjax”, [“POST”, url, details, xhr, headers, formData])
https://docs.webix.com/desktop__server_customload.html#modifyingbackgroundajaxrequests