I have backend endpoint Task and I need to call this endpoint from HttpClient. Currently I am getting Unsuppor
You need to specify parameter name in MultipartFormDataContent collection matching action parameter name (csvFile) and a random file name
var multipartContent = new MultipartFormDataContent();
multipartContent.Add(byteArrayContent, "csvFile", "filename");
var postResponse = await _client.PostAsync("offers", multipartContent);
or equivalent
var postResponse = await _client.PostAsync("offers", new MultipartFormDataContent {
{ byteArrayContent, "csvFile", "filename" }
});