SDL Trados 2019 with DeepL

When trying to add Deepl to the translation resources, we get this error message:

"There was a connection protocol error.

Please check that you have entered the correct port number and other settings.

<SDLErrorDetails time="10/09/2020 14:41:16">
  <ErrorMessage>There was a connection protocol error.
Please check that you have entered the correct port number and other settings.</ErrorMessage>
  <Exception>
    <Type>System.AggregateException, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</Type>
    <HelpLink />
    <Source>mscorlib</Source>
    <HResult>-2146233088</HResult>
    <StackTrace><![CDATA[   at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions)
   at System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)
   at System.Threading.Tasks.Task`1.get_Result()
   at Sdl.Community.DeepLMTProvider.DeepLTranslationProviderConnecter.GetSupportedLanguages(String type)
   at Sdl.Community.DeepLMTProvider.DeepLMtTranslationProvider.GetSupportedTargetLanguages(LanguagePair[] languagePairs)
   at Sdl.Community.DeepLMTProvider.DeepLMtTranslationProviderWinFormsUI.Browse(IWin32Window owner, LanguagePair[] languagePairs, ITranslationProviderCredentialStore credentialStore)
   at Sdl.TranslationStudio.Common.TranslationMemory.TranslationMemoriesControl.pluginContextMenuStripItem_Click(Object sender, EventArgs e)
   at System.Windows.Forms.ToolStripItem.RaiseEvent(Object key, EventArgs e)
   at System.Windows.Forms.ToolStripMenuItem.OnClick(EventArgs e)
   at System.Windows.Forms.ToolStripItem.HandleClick(EventArgs e)
   at System.Windows.Forms.ToolStripItem.HandleMouseUp(MouseEventArgs e)
   at System.Windows.Forms.ToolStripItem.FireEventInteractive(EventArgs e, ToolStripItemEventType met)
   at System.Windows.Forms.ToolStripItem.FireEvent(EventArgs e, ToolStripItemEventType met)
   at System.Windows.Forms.ToolStrip.OnMouseUp(MouseEventArgs mea)
   at System.Windows.Forms.ToolStripDropDown.OnMouseUp(MouseEventArgs mea)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
   at System.Windows.Forms.ToolStrip.WndProc(Message& m)
   at System.Windows.Forms.ToolStripDropDown.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)]]></StackTrace>
    <InnerException>
      <Type>System.Net.Http.HttpRequestException, System.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a</Type>
      <HelpLink />
      <Source />
      <HResult>-2146233088</HResult>
      <StackTrace><![CDATA[]]></StackTrace>
      <InnerException>
        <Type>System.Net.WebException, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</Type>
        <Status>ProtocolError</Status>
        <HelpLink />
        <Source>System</Source>
        <HResult>-2146233079</HResult>
        <StackTrace><![CDATA[   at System.Net.HttpWebRequest.EndGetRequestStream(IAsyncResult asyncResult, TransportContext& context)
   at System.Net.Http.HttpClientHandler.GetRequestStreamCallback(IAsyncResult ar)]]></StackTrace>
      </InnerException>
    </InnerException>
  </Exception>
  <Environment>
    <ProductName>SDL Trados Studio</ProductName>
    <ProductVersion>15.0.0.0</ProductVersion>
    <EntryAssemblyFileVersion>15.2.6.2831</EntryAssemblyFileVersion>
    <OperatingSystem>Microsoft Windows 10 Enterprise</OperatingSystem>
    <ServicePack>NULL</ServicePack>
    <OperatingSystemLanguage>1033</OperatingSystemLanguage>
    <CodePage>1252</CodePage>
    <LoggedOnUser>MSNET\FDD6900</LoggedOnUser>
    <DotNetFrameWork>4.0.30319.42000</DotNetFrameWork>
    <ComputerName>PO171507060</ComputerName>
    <ConnectedToNetwork>True</ConnectedToNetwork>
    <PhysicalMemory>8266320 MB</PhysicalMemory>
  </Environment>
</SDLErrorDetails>