Flutter error in Dio https request. HandshakeException: Handshake error in client OS Error: (TLSV1_ALERT_DECODE_ERROR(tls_record.cc:594))

I am trying to send a https request from flutter with following function:

Future<void> sendOTP(PhoneNumber phoneNumber) async {    try {      final String url = 'https://127.0.0.1:5432/api/send_otp';      final response = await _dio.post(        url,        data: {'number': 1234567890},        options: Options(          headers: {'Content-Type': 'application/json',          },        ),      );      if (response.statusCode != 200) {        throw Exception("Failed to send OTP: ${response.statusCode}");      }    } on DioError catch (e) {      throw Exception("Failed to send OTP: ${e.error.toString()}");    }  }

To enable ssl certificate I have added following code in my main method:

void main() async {  WidgetsFlutterBinding.ensureInitialized();  ByteData data = await PlatformAssetBundle().load('asset/certificate/certificate.pem');  SecurityContext.defaultContext      .setTrustedCertificatesBytes(data.buffer.asUint8List());  runApp(const MyApp());}

I have downloaded the certificate.pem file from https://letsencrypt.org/certs/lets-encrypt-r3.pem.

When I am sending the request using thunderclient or postman with the certificate, it works but from the flutter app it throws following error:

Error: HandshakeException: Handshake error in client (OS Error:    TLSV1_ALERT_DECODE_ERROR(tls_record.cc:594))

For server, I am using actix-web with rustls - if relevant. Please suggest how do I fix the same?