415 status code. Fetch() post with formData and Int params

Question

I am trying to do a fetch() post and send a FormData object and an Int. I can do one or the other but when trying to send both I get unrelating 415 status codes.

My post data looks like:

var payload = {
    documents: documents, // which is of type new FormData()
    applicationId: applicationId // which is of type int
}

method: "POST",
headers: {
    "Authorization": `Bearer ${accessToken}`
},
body: payload

And my c# backend looks like below:

[HttpPost]
public async Task<JsonResult> UploadDocuments(DocumentUploadVm payload)

below is my request headers:

:authority: localhost:44343
:method: POST
:path: /api/expert/UploadDocuments
:scheme: https
accept: */*
accept-encoding: gzip, deflate, br
accept-language: en-US,en;q=0.9
authorization: Bearer eyJraWQiOiJYNnplamszSy10RjBkMmtWYXpHNE84aFNsUGtSSklhT1ZMeGQ3dC1tQ21FIiwiYWxnIjoiUlMyNTYifQ.eyJ2ZXIiOjEsImp0aSI6IkFULnRuaGFQVGp5RnY4eEhMaGFVM18zLW5rdlVLWV9QUEw5aXJTczI4NHF3c3ciLCJpc3MiOiJodHRwczovL2Rldi04NzAzMTAub2t0YS5jb20vb2F1dGgyL2RlZmF1bHQiLCJhdWQiOiJhcGk6Ly9kZWZhdWx0IiwiaWF0IjoxNjAwNjQ0MzAzLCJleHAiOjE2MDA2NDc5MDMsImNpZCI6IjBvYXAzbmdtNG1BUDBTT1YzNHg2IiwidWlkIjoiMDB1ZGFudnVpUjB6SHp6emk0eDYiLCJzY3AiOlsicHJvZmlsZSIsImdyb3VwcyIsImVtYWlsIiwib3BlbmlkIiwicGhvbmUiXSwic3ViIjoiZGFuaWVsOTVicm93bkBnbWFpbC5jb20ifQ.0ya1CTLuPQcPLyXgph7TQMzwhWtUWrb1QzQx6G2kS4X5fawXZ13XFIztG2TMjCIrTrbGa1WPx-hYmqI7EB2Eilhp0ekQKt85U7Q3Ug5HuQQMhrH8KjvHF5fhElNwf5z1vp4Zgtg1MbF-MPetoV4ttG3SQwxLJ-SFHZFkA-HY2lzoMQS-40V53q5ruVbeXEpX8iwhSXzA7mp53YEaSNWecDJxHoBy6yXszrJrpkQ1wqsp9p5ti1XASVczlLkL-J-IOx6Rf61LfPH9_Q4KR3aZsd_peInJF14YF0lLesmxcnQcvbdMGsUO0PrPtku8wQEeuuQGYn-zZR5eBSDR9ZbzLw
content-length: 15
content-type: text/plain;charset=UTF-8
origin: http://localhost:8080
referer: http://localhost:8080/expert/register
sec-fetch-dest: empty
sec-fetch-mode: cors
sec-fetch-site: cross-site
user-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/85.0.4183.102 Safari/537.36

I have tried using the [FromBody],[FromForm] tags, stringifying and everything in between to no avail. Any help would be greeeeeeeatly appreciated as I am losing my mind.