Icon does not appear for Outlook Web add in for Outlook 2016 on Windows

I am developing a Web Add In for Outlook. I have specified the IconUrl for the add in. The add in appears in Outlook for Windows. However it loads the default icon instead of my personalised icon.

Here is my XML manifest

<?xml version="1.0" encoding="UTF-8"?>
<!--Created:ce44715c-8c4e-446b-879c-ea9ebe0f09c8-->
<OfficeApp
          xmlns="http://schemas.microsoft.com/office/appforoffice/1.1"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xmlns:bt="http://schemas.microsoft.com/office/officeappbasictypes/1.0"
          xmlns:mailappor="http://schemas.microsoft.com/office/mailappversionoverrides/1.0"
          xsi:type="MailApp">

  <!-- Begin Basic Settings: Add-in metadata, used for all versions of Office unless override provided. -->

  <!-- IMPORTANT! Id must be unique for your add-in, if you reuse this manifest ensure that you change this id to a new GUID. -->
  <Id>badb297b-b8e8-41e1-9513-ff821c15189c</Id>

  <!--Version. Updates from the store only get triggered if there is a version change. -->
  <Version>1.0.0.0</Version>
  <ProviderName>my company- Meetings</ProviderName>
  <DefaultLocale>en-US</DefaultLocale>
  <!-- The display name of your add-in. Used on the store and various places of the Office UI such as the add-ins dialog. -->
  <DisplayName DefaultValue="My Company" />
  <Description DefaultValue="Outlook addin"/>  
  <IconUrl DefaultValue="https://localhost:44373/Images/Icon80.png"/>