flutter ios 에서 webview 진입시 다음과 같은 메시지가 발생합니다.

[ERROR:flutter/runtime/dart_vm_initializer.cc(40)] Unhandled Exception: PlatformException(evaluateJavaScript_failed, Failed evaluating JavaScript, JavaScript string was: '          var clientKey = '****';
          var tossPayments = TossPayments(clientKey);
          tossPayments.requestPayment('계좌이체', {"paymentMethod":"계좌이체","amount":62700,"orderId":"ORDER-example","orderName":"example","successUrl":"tosspayments://payment/flutter/success","failUrl":"tosspayments://payment/flutter/fail","customerName":"****","customerMobilePhone":"*****"});
          '
Error Domain=WKErrorDomain Code=5 "JavaScript execution returned a result of an unsupported type" UserInfo={NSLocalizedDescription=JavaScript execution returned a result of an unsupported type}, null)
#0      StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:646:7)
message_codecs.dart:646
#1      MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:334:18<…>