I've come across a couple similar posts related to JSON decoding errors, but I think my problem is different enough to ask it:

Model

struct UserSLPForgotPasswordRequest: Codable {
    var email: String
}

struct UserSLPForgotPassword: Codable {
    let email: String
}

API Service Session/Encoding

URLSession.shared.dataTask(with: request) { (data, response, error) in

            if data != nil { print(data!) }

            if response != nil { print(response!) }

            if error != nil { print(response!) }

            guard let httpResponse = response as? HTTPURLResponse, (200...299).contains(httpResponse.statusCode) else {
                completion(.failure(.custom(errorMessage: "Non-200 Response")))
//                print(response!)
                return
            }
            guard let data = data, error == nil else {
                completion(.failure(.custom(errorMessage: "No Data")))
                return
            }
            self.decode(data: data, completion: completion)

        }.resume()

Generic Decoder

    private func decode<T: Decodable>(data: Data, completion: @escaping (Result<T, AuthenticationError>) -> Void) {
        do {
            let jsonDecoded = try JSONDecoder().decode(T.self, from: data)
            completion(.success(jsonDecoded))
        } catch (let error) {
            print(error)
            completion(.failure(.decodingError))
        }
    }

Somewhere inside the decoder function I recieve this error:

dataCorrupted(Swift.DecodingError.Context(codingPath: [], debugDescription: "The given data was not valid JSON.", underlyingError: Optional(Error Domain=NSCocoaErrorDomain Code=3840 "Invalid value around line 1, column 0." UserInfo={NSDebugDescription=Invalid value around line 1, column 0., NSJSONSerializationErrorIndex=0})))

My back-end is working fine and sending me a 200 response, but I'm just not sure where the decoder is having its problems with the JSON.

I have only used the decoder with GET and POST requests that have multiple fields involved and this particular endpoint only receives a single field and technically isn't returning anything, so maybe it's something to do with that? IDK...

Please post a sample of the JSON response. There is something in there the decoder doesn't like, right at the very beginning.