1) Разрешение подключения по http (без ssl).

Android: Manifest

IOS:
Добавить

<key>NSAppTransportSecurity</key>
<dict>
    <key>NSAllowsArbitraryLoads</key>
    <true/>
</dict>

The resource could not be loaded because the App Transport Security policy requires the use of a secure connection
https://stackoverflow.com/questions/32631184/the-resource-could-not-be-loaded-because-the-app-transport-security-policy-requi


2) Доступ к файлам. Android

Manifest

Xamarin forms: How to create folder and a file in device external storage?
https://stackoverflow.com/questions/66469608/xamarin-forms-how-to-create-folder-and-a-file-in-device-external-storage

Xamarin-System.UnauthorizedAccessException: Access to the path is denied
https://stackoverflow.com/questions/46911486/xamarin-system-unauthorizedaccessexception-access-to-the-path-is-denied

Access to the path "/storage/emulated/0/NewTxt.txt" is denied.'
https://social.msdn.microsoft.com/Forums/en-US/5931f217-8590-4289-8a33-c9a5c07faf50/access-to-the-path-quotstorageemulated0newtxttxtquot-is-denied?forum=xamarinforms

Can't write to Android External storage even with permissions set
https://stackoverflow.com/questions/60569224/cant-write-to-android-external-storage-even-with-permissions-set/60594975#60594975

//Пример кода с явным запросом прав на доступ
var PackageName = AppInfo.PackageName;
var requiredPermissions = new string[] {
 Manifest.Permission.ReadExternalStorage,
 Manifest.Permission.WriteExternalStorage
};

var needPermissionRequest = false;
foreach (var elem in requiredPermissions)
{
if (PackageManager.CheckPermission(elem, PackageName) != Permission.Granted)
 {
  needPermissionRequest = true;
 }
}

if (needPermissionRequest)
{
 RequestPermissions(
  requiredPermissions,
 1
  );
}
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