Swift JSON Encode Issue

I am trying to decode some JSON in swift, but I keep getting an error, which I am assuming is because my struct is not written correctly. Any ideas? I am calling this API https://pokeapi.co/api/v2/pokemon/1/

Here is the json decode call:

func fetchPokemonImages() {
        
        for var pokemons in self.Pokemons {
            
            let defaultSession = URLSession(configuration: .default)
            if let url = URL(string: pokemons.url) {
              let request = URLRequest(url: url)
              let dataTask = defaultSession.dataTask(with: request) { (data, response, error) in
                guard let pokemonImage = try? JSONDecoder().decode(PokemonImageList.self, from: data!) else {
                  print(error)
                  return
                }
                DispatchQueue.main.async {
                    
                    self.PokemonsImage.append(contentsOf: pokemonImage.sprites)
                    self.PokemonTableView.reloadData()             }
              }
                dataTask.resume()
            }
        }
    }

Here are my structs:

struct PokemonImage: Codable {
    let back_default: String

    enum CodingKeys: String, CodingKey {
        case backDefault = "back_default"
    }

    init(backDefault: String) {
        self.backDefault = backDefault
    }

    init(from decoder: Decoder) throws {
        let postsContainer = try decoder.container(keyedBy: CodingKeys.self)
        backDefault = try postsContainer.decode(String.self, forKey: .backDefault)
    }
}

struct PokemonImageList: Codable {
    
    let sprites: [PokemonImage]

    enum CodingKeys: String, CodingKey {
        case sprites
    }
}