How to POST to google form by Flutter. The response is always 400 (POSTMAN'S result is 200 OK)

After reproduce your case in Postman with form-data:

and for control, i'm using curl for testing :

curl --location --request POST 'https://docs.google.com/forms/u/0/d/e/1FAIpQLSc5aAwiiLJ2qJhF-ngGFfRl8m8yEJs8gTipY7pnNQkxGcJ_1w/formResponse' \    --form 'entry.844954850=bug' \    --form 'entry.479013015=dsfa'

now i can reproduce this Post request in flutter:

void _request() async {  String url =      'https://docs.google.com/forms/u/0/d/e/1FAIpQLSc5aAwiiLJ2qJhF-ngGFfRl8m8yEJs8gTipY7pnNQkxGcJ_1w/formResponse';  Map<String, String> headers = {    "Content-Type": "application/x-www-form-urlencoded",  };  // String body = json.encode(...)      //------------> Before  Map<String, String> requestBody = <String, String>{ // After    'entry.844954850': 'bug',    'entry.479013015': 'dsfa'  };  http.Response resp =      await http.post(url, headers: headers, body: requestBody);  print(resp);  if (resp.statusCode != 200) {    print('Failed to post ${resp.statusCode}');  } else {    print(resp.body);  }}

status code in debug mode:

For dio, it's same replace json and your request is formatted correctly.