Argument passed to call that takes no arguments error for Structs within Structs

Hi all so I need to call a function that takes in the following parameters:

 let params = [
                "inputParameters" : ["A2":"a1","B1":"b1","C1":"c1","D1":"d1"]
            ]

so I made the following encodable struct for it

 struct Parameters2 : Encodable{

             let inputparameters = inputParameters(A1: "", B1: "", C1: "", D1: "")
            }

 struct inputParameters: Encodable {

                let A1: String
                let B1: String
                let C1: String
                let D1: String
            }

However when I call

guard let params = Parameters2(inputParameters(A1:"something", B1:"something", C1:"something", D1:"something"))
            else{
                return
            }

I get an error 'Argument passed to call that takes no arguments' even though I clearly defined the input arguments in the struct. Can anyone figure out what could be going wrong?

EDIT: Upon @vadian's suggestions I'm adding the function where this parameter is plugged into:

            func executePost(parameters: Parameters2, completion: @escaping (Any?, Error?) -> Void) {
            AF.request("myURL",
                       method: .post,
                       parameters: parameters,
                       encoder: JSONParameterEncoder.default, headers: headers).response { response in
                debug print(response)
                
                
                if let error = response.error {
                    completion(nil, error)
                }
                else if let jsonArray = response.value as? Any{
                    completion(jsonArray, nil)
                }
                else if let jsonDict = response.value as? Any{
                    completion([jsonDict], nil )
                }
                
            }}

And I call the function as follows:

  executePost(parameters: JSONEncoder().encode(params)) { (json, error) in <-- error Cannot convert value of type 'Data' to expected argument type '[String : InputParameters]'
                if let error = error{
                    print(error.localizedDescription)
                    
                }
                else if let json = json {

                    print(json)
                   
                }
            }

Solution

Your code doesn't work for several reasons:

A key mismatch inputParameters (dictionary key) vs. inputparameters (struct member).
The mentioned error which occurs because you assigned a default value in Parameters2.
guard let expects an optional, but there is none.

An easier way is one struct

struct InputParameters: Encodable {
      let A1, B1, C1, D1: String
}

and a literal dictionary key

let params = ["inputParameters": InputParameters(A1:"something", B1:"something", C1:"something", D1:"something")]

and encode params