How to send byte array in c# ApiController

I would base64 encode the byte arrays and change your model properties from byte[] to string. That should allow you to post these strings to your controller where you can convert them back to byte arrays.

To encode as base64 string use string byteString = Convert.ToBase64String(byteArray) and convert back using byte[] byteArray = Convert.FromBase64String(byteString).

Your updated code might look something like:

public class TestData{    public string PreviewImage { get; set; }    public string FileAsByteArray { get; set; }}[Route("function-route")][HttpPost]public HttpResponseMessage Testfunction(TestData t_testData){    // convert base64 string to byte[]    byte[] preview = Convert.FromBase64String(t_testData.PreviewImage);    byte[] file = Convert.FromBase64String(t_testData.FileAsByteArray);    ...    HttpResponseMessage httpResponseMessage = Request.CreateResponse(HttpStatusCode.OK);    return httpResponseMessage;}

To test using postman you can use javascript functions atob() and btoa() to convert a byte array to a base 64 encoded string and vice versa.