This is a POST request. You cannot make POST requests with your web browser.
No change in this endpoint for a long time, and a quick test shows that it works just fine. I've used this code to copy the selected file(s) to a folder in my database:
IMWS.post('v1/files/copy',{
idlist: IMatch.idlist.fileWindowSelection,
targetpath: 'C:\\data\\Image\\Test',
}).then(function(response) {
console.log(JSON.stringify(response,null,2));
},function(error) {
console.log(JSON.stringify(error,null,2));
});