What solved it for me was using Dio with native IO plugin.

Example

import 'package:native_dio_adapter/native_dio_adapter.dart';
import 'package:dio/dio.dart';

Dio client = Dio();
client.httpClientAdapter = NativeAdapter(
      createCupertinoConfiguration: () => URLSessionConfiguration.ephemeralSessionConfiguration()
        ..allowsCellularAccess = true
        ..allowsConstrainedNetworkAccess = true
        ..allowsExpensiveNetworkAccess = true,
    );

var request = await client.post<Map<String, dynamic>>(Uri.parse(baseUrl + path).toString(),
 data: convert.jsonEncode(body),
 options: Options(
 headers: {"Content-Type": "application/json"},
));

It works because on Appclip, dart IO is blocked from accessing internet, don't know why, but if requests go though native platform it works fine.