Custom encoding and decoding of JSON data. Wouldn't necessary recommend this as your models should mirror your API.

CustomEncodingDecoding.swift

import Swift
import Foundation

let json = """
{
    "amount": 3,
    "confirmed": false,
    "context": {
        "wishlist": {
                "mTy7R1Y7OI22w1jAqKvo": {
                    "id": "12345",
                    "confirmed": true
                }
            },
        "wish": {
            "mTy7R1Y7OI22w1jAqKvo": {
                "id": "12345",
                "confirmed": true
            }
        }
    }
}
"""



struct Wish: Codable {
    let id: String?
    let confirmed: Bool
}

struct Wishlist: Codable {
    let id: String?
    let confirmed: Bool
}

struct CodableObject: Codable {
    let amount: Int
    let confirmed: Bool
    let context: Context
    
    struct Context: Codable {
        let wishlist: Wishlist
        let wish: Wish
        
        init(wishlist: Wishlist, wish: Wish) {
            self.wishlist = wishlist
            self.wish = wish
        }
        
        struct DynamicKeys: CodingKey {
            var stringValue: String
            init?(stringValue: String) {
                self.stringValue = stringValue
            }
            var intValue: Int? { return nil }
            init?(intValue: Int) { return nil }
            static let wishlist = DynamicKeys(stringValue: "wishlist")!
            static let wish = DynamicKeys(stringValue: "wish")!
        }
        
        func encode(to encoder: Encoder) throws {
            var container = encoder.container(keyedBy: DynamicKeys.self)
            if let wishlistId = wishlist.id {
                try container.encode([wishlistId: wishlist], forKey: DynamicKeys.wishlist)
            }
            if let wishId = wish.id {
                try container.encode([wishId: wish], forKey:  DynamicKeys.wish)
            }
        }
        
        init(from decoder: Decoder) throws {
            let container = try decoder.container(keyedBy: DynamicKeys.self)
            
            var wishlistValueDict: [String: Wishlist]?
            var wishValueDict: [String: Wish]?
            
            for key in container.allKeys {
                switch key.stringValue {
                case DynamicKeys.wishlist.stringValue:
                    wishlistValueDict = try container.decode([String: Wishlist].self, forKey: key)
                    
                case DynamicKeys.wish.stringValue:
                    wishValueDict = try container.decode([String: Wish].self, forKey: key)
                default:
                    throw NSError(domain: "Keys not found", code: 0, userInfo: nil)
                }
            }
            
            guard let wishlist = wishlistValueDict?.values.first,
            let wish = wishValueDict?.values.first else {
                throw NSError(domain: "Could not decode keys", code: 0, userInfo: nil)
            }
            
            self.wish = wish
            self.wishlist = wishlist
        }
    }
}


let object = CodableObject(amount: 3, confirmed: true, context: CodableObject.Context(wishlist: Wishlist(id: "234870982314782347", confirmed: true), wish: Wish(id: "83217409872139847", confirmed: false)))
let encoder = JSONEncoder()
if let json = try? encoder.encode(object) {
    print(String(data: json, encoding: .utf8)!)
    
    do {
        let results = try JSONDecoder().decode(CodableObject.self, from: json)
        print(results.context.wish.id)
        print(results.context.wishlist.id)
    } catch {
        print(error)
    }
}