In case someone would need - to achieve same or similar thing(like delete) via POST instead of FromUri, use FromBody and on client side(JS/jQuery) format param as $.param({ '': categoryids }, true)
c#:
public IHttpActionResult Remove([FromBody] int[] categoryIds) jQuery:
$.ajax({ type: 'POST', data: $.param({ '': categoryids }, true), url: url, //... }); The thing with $.param({ '': categoryids }, true) is that it .net will expect post body to contain urlencoded value like =1&=2&=3 without parameter name, and without brackets.