我想目前还没有正式的方案。
如何尝试使用直接API使用http或dio

import 'package:http/http.dart' as http;

final String baseUrl = 'https://api.us.afterpay.com/v2/checkouts';
final String merchantId = '<your-merchant-id>';
final String secretKey = '<your-secret-key>';

Future<http.Response> createOrder(double amount, String currency, String 
                      reference) async {                        

 Map<String, dynamic> requestBody = {
                                    "amount": {
                                           "amount": "100.00",
                                           "currency": "USD"
                                             },
                                    "mode": "express",
                                    "merchant": {                                     
                                 "popupOriginUrl":"https://www.afterpay-merchant.com/cart"
                                              }
                           };
           return await http.post(Uri.parse(url),
           headers: {'accept': 'application/json','Content-Type':'application/json'},
           body: jsonEncode(requestBody));
     }

从响应中，您必须处理成功或失败，并保存订单ID以供将来使用和参考。