Try to include Net.Http...

build.bat

@@ -210,7 +210,9 @@ COPY /Y /V "UtfUnknown.dll"                        "temp_zip\"
 COPY /Y /V "Vosk.dll"                              "temp_zip\"
 COPY /Y /V "NCalc.dll"                             "temp_zip\"
 COPY /Y /V "..\..\DLLs\Interop.QuartzTypeLib.dll"  "temp_zip\"
+COPY /Y /V "System.Net.Http.Extensions.dll"        "temp_zip\"
 COPY /Y /V "Newtonsoft.Json.dll"                   "temp_zip\"
+COPY /Y /V "System.Net.Http.Primitives.dll"        "temp_zip\"
 COPY /Y /V "NAudio.Core.dll"                       "temp_zip\"
 COPY /Y /V "NAudio.WinMM.dll"                      "temp_zip\"
 COPY /Y /V "Microsoft.Win32.Registry.dll"          "temp_zip\"

build_beta.bat

@@ -184,7 +184,9 @@ COPY /Y /V "UtfUnknown.dll"                        "temp_zip\"
 COPY /Y /V "Vosk.dll"                              "temp_zip\"
 COPY /Y /V "NCalc.dll"                             "temp_zip\"
 COPY /Y /V "..\..\DLLs\Interop.QuartzTypeLib.dll"  "temp_zip\"
+COPY /Y /V "System.Net.Http.Extensions.dll"        "temp_zip\"
 COPY /Y /V "Newtonsoft.Json.dll"                   "temp_zip\"
+COPY /Y /V "System.Net.Http.Primitives.dll"        "temp_zip\"
 COPY /Y /V "NAudio.Core.dll"                       "temp_zip\"
 COPY /Y /V "NAudio.WinMM.dll"                      "temp_zip\"
 COPY /Y /V "Microsoft.Win32.Registry.dll"          "temp_zip\"

installer/Subtitle_Edit_Installer.iss

@@ -322,6 +322,8 @@ Source: {#bindir}\Vosk.dll;                        DestDir: {app};
 Source: {#bindir}\NCalc.dll;                       DestDir: {app};                                    Flags: ignoreversion; Components: main
 Source: ..\src\ui\DLLs\Interop.QuartzTypeLib.dll;  DestDir: {app};                                    Flags: ignoreversion; Components: main
 Source: {#bindir}\Newtonsoft.Json.dll;             DestDir: {app};                                    Flags: ignoreversion; Components: main
+Source: {#bindir}\System.Net.Http.Extensions.dll;  DestDir: {app};                                    Flags: ignoreversion; Components: main
+Source: {#bindir}\System.Net.Http.Primitives.dll;  DestDir: {app};                                    Flags: ignoreversion; Components: main
 Source: {#bindir}\NAudio.Core.dll;                 DestDir: {app};                                    Flags: ignoreversion; Components: main
 Source: {#bindir}\NAudio.WinMM.dll;                DestDir: {app};                                    Flags: ignoreversion; Components: main
 Source: {#bindir}\Microsoft.Win32.Registry.dll;    DestDir: {app};                                    Flags: ignoreversion; Components: main

src/ui/Properties/Settings.Designer.cs

@@ -12,7 +12,7 @@ namespace Nikse.SubtitleEdit.Properties {
     
     
     [global::System.Runtime.CompilerServices.CompilerGeneratedAttribute()]
-    [global::System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.VisualStudio.Editors.SettingsDesigner.SettingsSingleFileGenerator", "17.1.0.0")]
+    [global::System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.VisualStudio.Editors.SettingsDesigner.SettingsSingleFileGenerator", "17.7.0.0")]
     internal sealed partial class Settings : global::System.Configuration.ApplicationSettingsBase {
         
         private static Settings defaultInstance = ((Settings)(global::System.Configuration.ApplicationSettingsBase.Synchronized(new Settings())));

src/ui/SubtitleEdit.csproj

@@ -85,6 +85,12 @@
     <Reference Include="System.Drawing" />
     <Reference Include="System.EnterpriseServices" />
     <Reference Include="System.Net.Http" />
+    <Reference Include="System.Net.Http.Extensions, Version=2.2.29.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL">
+      <HintPath>..\..\packages\Microsoft.Net.Http.2.2.29\lib\net45\System.Net.Http.Extensions.dll</HintPath>
+    </Reference>
+    <Reference Include="System.Net.Http.Primitives, Version=4.2.29.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL">
+      <HintPath>..\..\packages\Microsoft.Net.Http.2.2.29\lib\net45\System.Net.Http.Primitives.dll</HintPath>
+    </Reference>
     <Reference Include="System.Net.Http.WebRequest" />
     <Reference Include="System.Security.AccessControl, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a, processorArchitecture=MSIL">
       <HintPath>..\..\packages\System.Security.AccessControl.6.0.0\lib\net461\System.Security.AccessControl.dll</HintPath>
@@ -2574,13 +2580,6 @@
       <Install>true</Install>
     </BootstrapperPackage>
   </ItemGroup>
-  <ItemGroup>
-    <ProjectReference Include="..\libse\LibSE.csproj">
-      <Project>{3e3cb28f-3a7b-430f-9eb3-0d6c1e53b753}</Project>
-      <Name>LibSE</Name>
-      <Private>True</Private>
-    </ProjectReference>
-  </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <ItemGroup>
     <HunspellAssemblies Include="Hunspellx64.dll">
@@ -2590,6 +2589,13 @@
       <Visible>false</Visible>
     </HunspellAssemblies>
   </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\libse\LibSE.csproj" AdditionalProperties="TargetFramework=net48">
+      <SetTargetFramework>TargetFramework=net48</SetTargetFramework>
+      <Project>{d6f64cd3-c3ea-4b36-b575-9b3b8a3ca13f}</Project>
+      <Name>LibSE</Name>
+    </ProjectReference>
+  </ItemGroup>
   <Target Name="BeforeCompile">
     <XmlPeek XmlInputPath="$(SolutionDir)\src\ui\packages.config" Query="//package[@id='NHunspell']/@version">
       <Output TaskParameter="Result" PropertyName="HunspellVersion" />
@@ -2608,6 +2614,8 @@
       <ErrorText>This project references NuGet package(s) that are missing on this computer. Use NuGet Package Restore to download them.  For more information, see http://go.microsoft.com/fwlink/?LinkID=322105. The missing file is {0}.</ErrorText>
     </PropertyGroup>
     <Error Condition="!Exists('..\..\packages\Vosk.0.3.38\build\Vosk.targets')" Text="$([System.String]::Format('$(ErrorText)', '..\..\packages\Vosk.0.3.38\build\Vosk.targets'))" />
+    <Error Condition="!Exists('..\..\packages\Microsoft.Bcl.Build.1.0.21\build\Microsoft.Bcl.Build.targets')" Text="$([System.String]::Format('$(ErrorText)', '..\..\packages\Microsoft.Bcl.Build.1.0.21\build\Microsoft.Bcl.Build.targets'))" />
   </Target>
   <Import Project="..\..\packages\Vosk.0.3.38\build\Vosk.targets" Condition="Exists('..\..\packages\Vosk.0.3.38\build\Vosk.targets')" />
+  <Import Project="..\..\packages\Microsoft.Bcl.Build.1.0.21\build\Microsoft.Bcl.Build.targets" Condition="Exists('..\..\packages\Microsoft.Bcl.Build.1.0.21\build\Microsoft.Bcl.Build.targets')" />
 </Project>

src/ui/packages.config

@@ -1,5 +1,8 @@
 <?xml version="1.0" encoding="utf-8"?>
 <packages>
+  <package id="Microsoft.Bcl" version="1.1.10" targetFramework="net48" />
+  <package id="Microsoft.Bcl.Build" version="1.0.21" targetFramework="net48" />
+  <package id="Microsoft.Net.Http" version="2.2.29" targetFramework="net48" />
   <package id="Microsoft.Win32.Registry" version="5.0.0" targetFramework="net48" />
   <package id="NAudio.Core" version="2.2.0" targetFramework="net48" />
   <package id="NAudio.WinMM" version="2.2.0" targetFramework="net48" />