Variable was never mutated...or Constant being used before initialized

I'm wanting to get jsonMeals data back and use it outside of this function. However it seems no matter where I place my JSON variable I get an error. Changing it to a let does as well although a different one. Any insight would be greatly appreciated!

Error:

Constant 'json' used before being initialized // Variable 'json' was never mutated; consider changing to 'let' constant

func getApiDetailData(completed: @escaping () -> ()) {
    var json: Any?
    let urlString = "https://www.themealdb.com/api/json/v1/1/lookup.php?i=\(id)"
    let url = URL(string: urlString)
    
    URLSession.shared.dataTask(with: url!) { (data, response, error) in
            do {
                let json = try JSONSerialization.jsonObject(with: data!)
                print("\(json)Testing")
                DispatchQueue.main.async {
                    completed()
                }
            }
            catch {
                print("Error getting detail JSON data:\(error)")
            }
        guard let json = json as? [String : Any],
              let jsonMeals = json["meals"] as? [String: Any] else {
                  print("No meals in json \(error?.localizedDescription)")
                return
            }
        print("testing jsonMeals\(jsonMeals)")
    }.resume()
}

try something like this example code:

func getApiDetailData(completed: @escaping () -> ()) {
    //   var json: Any?   // <-- remove, never used
    let urlString = "https://www.themealdb.com/api/json/v1/1/lookup.php?i=\(id)"
    let url = URL(string: urlString)
    
    URLSession.shared.dataTask(with: url!) { (data, response, error) in
        do {
            let jsonData = try JSONSerialization.jsonObject(with: data!)
            print("\(jsonData) Testing")
            
            guard let json = jsonData as? [String : Any],
                  let jsonMeals = json["meals"] as? [[String: Any]] else {
                print("No meals in json \(error?.localizedDescription)")
                completed()  // <-- here
                return
            }
            print("testing jsonMeals \(jsonMeals)")
            completed()  // <-- here
        }
        catch {
            print("Error getting detail JSON data:\(error)")
            completed()  // <-- here
        }
    }.resume()
}

Or, if you want to return the jsonMeals results:

func getApiDetailData(completed: @escaping ([[String: Any]]?) -> ()) {  // <-- here
  //  var json: Any?   // <-- remove, never used
    let urlString = "https://www.themealdb.com/api/json/v1/1/lookup.php?i=\(id)"
    let url = URL(string: urlString)
    
    URLSession.shared.dataTask(with: url!) { (data, response, error) in
        do {
            let jsonData = try JSONSerialization.jsonObject(with: data!)
            print("\(jsonData) Testing")
            
            guard let json = jsonData as? [String : Any],
                  let jsonMeals = json["meals"] as? [[String: Any]] else {
                print("No meals in json \(error?.localizedDescription)")
                completed(nil)  // <-- here
                return
            }
            print("testing jsonMeals \(jsonMeals)")
            completed(jsonMeals)  // <-- here
        }
        catch {
            print("Error getting detail JSON data:\(error)")
            completed(nil)  // <-- here
        }
    }.resume()
}