TRON not using request.header - httprequest

Question

I am using Xcode 8.3.3 (8E3004b)
I am using TRON (which includes Alamofire) to make HTTP Request to my REST API.
I have been successful getting a simple API working with this setup. I am trying to connect to a different API, which requires me to set the headers. It is this API that is throwing a Status 415 server error.
I have the following code to make the request via TRON. According to the TRON Github page, I should be ae to set the header like this:
request.headers = ["Content-Type":"application/json"]
I have also tried:
request.headerBuilder.headers(forAuthorizationRequirement: AuthorizationRequirement.allowed, including: ["Content-Type":"application/json"])
I tried adding a few different ways of writing that, but nothing seems to work.
Here's a bigger section of the code so you can see the context
let urlSubfix = "\(Constant.REST_MOBILE)\(Constant.REGISTER)"
let request: APIRequest<RegisterApiResult, JSONError> = tron.request(urlSubfix)
request.method = .put
// request.headers = ["Content-Type":"application/json"]
let header = request.headerBuilder.headers(forAuthorizationRequirement: AuthorizationRequirement.allowed, including: ["Content-Type":"application/json"])
request.headers = header
request.perform(withSuccess: { (registerApiResult) in
print("Successfully fetched our json object")
completion(registerApiResult)
}) { (err) in
print("Failed to fetch json...", err)
}
Here is the actual error from my log:
Failed to fetch json... APIError<JSONError>(request: Optional(http://www.slsdist.com/eslsd5/rest/mobileservice/register), response: Optional(<NSHTTPURLResponse: 0x618000028c20> { URL: http://www.slsdist.com/eslsd5/rest/mobileservice/register } { status code: 415, headers {
"Content-Length" = 0;
Date = "Sat, 22 Jul 2017 22:23:14 GMT";
Server = "Microsoft-IIS/7.5";
"X-Powered-By" = "Undertow/1, ASP.NET";
} }), data: Optional(0 bytes), error: Optional(Alamofire.AFError.responseValidationFailed(Alamofire.AFError.ResponseValidationFailureReason.unacceptableStatusCode(415))), errorModel: Optional(Go_Cart.Service.JSONError))
As you can see I have tried to set the headers a couple different ways, but neither of them seems to take affect. Any help or advice from anyone would be helpful.
Thanks in advance.