Office 365 PowerPoint online add-in not showing on the ribbon

[superblaettler]

We built Office 365 Add-Ins for Outlook, Word and PowerPoint. They look and work ok on the desktop. We install them via Admin Portal => "Integrated apps". This works ok for Outlook and Word online in the browser. But the PowerPoint App does not show up.
I've tried Chrome and Edge. Incognito and not.
It's working on the Desktop for Windows and Mac.

Any idea what we are missing?

This is the manifest for it:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<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:ov="http://schemas.microsoft.com/office/taskpaneappversionoverrides" xsi:type="TaskPaneApp">
  <Id>df719a2c-f205-406a-89ff-7a2cc19df0e3</Id>
  <Version>1.0.8.0</Version>
  <ProviderName>Supertext</ProviderName>
  <!-- FIXME: Do we want to localize DisplayName and Description? -->
  <DefaultLocale>en-US</DefaultLocale>
  <DisplayName DefaultValue="Supertext Translator"/>
  <Description DefaultValue="Automatically translate PowerPoint presentations. AI Translation powered by Supertext"/>
   <!-- TODO: Make sure all occurrences of production.ai-office-add-in.supertext.com are changed to your current deployment url before distributing the manifest -->
  <IconUrl DefaultValue="https://production.ai-office-add-in.supertext.com/assets/icon-32.png"/>
  <HighResolutionIconUrl DefaultValue="https://production.ai-office-add-in.supertext.com/assets/icon-64.png"/>
  <SupportUrl DefaultValue="https://www.supertext.com/en/contact"/>
  <AppDomains>
    <AppDomain>https://www.supertext.com</AppDomain>
  </AppDomains>
  <Hosts>
    <Host Name="Presentation"/>
  </Hosts>
    <Requirements>
      <Sets>
        <Set Name="PowerPointApi" MinVersion="1.1"/>
        <Set Name="DialogApi" MinVersion="1.1"/>
        <Set Name="DocumentEvents" MinVersion="1.1"/>
        <Set Name="CompressedFile" MinVersion="1.1"/>
        <Set Name="File" MinVersion="1.1"/>
        <Set Name="TextCoercion" MinVersion="1.1"/>
      </Sets>
    </Requirements> 
    <DefaultSettings>
      <SourceLocation DefaultValue="https://production.ai-office-add-in.supertext.com/taskpane.html"/>
    </DefaultSettings>
    <Permissions>ReadWriteDocument</Permissions>
    <VersionOverrides xmlns="http://schemas.microsoft.com/office/taskpaneappversionoverrides" xsi:type="VersionOverridesV1_0">
    <Hosts>
      <Host xsi:type="Presentation">
        <DesktopFormFactor>
           <ExtensionPoint xsi:type="PrimaryCommandSurface">
            <OfficeTab id="TabHome">
              <Group id="CommandsGroup">
                <Label resid="CommandsGroup.Label"/>
                <Icon>
                    <bt:Image size="16" resid="Icon.16x16"/>
                    <bt:Image size="32" resid="Icon.32x32"/>
                    <bt:Image size="48" resid="Icon.48x48"/>
                    <bt:Image size="64" resid="Icon.64x64"/>
                    <bt:Image size="80" resid="Icon.80x80"/>
                </Icon>
                <Control xsi:type="Button" id="TaskpaneButton">
                  <Label resid="TaskpaneButton.Label"/>
                  <Supertip>
                    <Title resid="TaskpaneButton.Label"/>
                    <Description resid="TaskpaneButton.Tooltip"/>
                  </Supertip>
                  <Icon>
                    <bt:Image size="16" resid="Icon.16x16"/>
                    <bt:Image size="32" resid="Icon.32x32"/>
                    <bt:Image size="48" resid="Icon.48x48"/>
                    <bt:Image size="64" resid="Icon.64x64"/>
                    <bt:Image size="80" resid="Icon.80x80"/>
                  </Icon>
                  <Action xsi:type="ShowTaskpane">
                    <SourceLocation resid="Taskpane.Url"/>
                  </Action>
                </Control>
              </Group>
            </OfficeTab>
          </ExtensionPoint>
        </DesktopFormFactor>
      </Host>
    </Hosts>
    <Resources>
      <bt:Images>
        <bt:Image id="Icon.16x16" DefaultValue="https://production.ai-office-add-in.supertext.com/assets/icon-16.png"/>
        <bt:Image id="Icon.32x32" DefaultValue="https://production.ai-office-add-in.supertext.com/assets/icon-32.png"/>
        <bt:Image id="Icon.48x48" DefaultValue="https://production.ai-office-add-in.supertext.com/assets/icon-48.png"/>
        <bt:Image id="Icon.64x64" DefaultValue="https://production.ai-office-add-in.supertext.com/assets/icon-64.png"/>
        <bt:Image id="Icon.80x80" DefaultValue="https://production.ai-office-add-in.supertext.com/assets/icon-80.png"/>
      </bt:Images>
      <bt:Urls>
        <bt:Url id="Taskpane.Url" DefaultValue="https://production.ai-office-add-in.supertext.com/taskpane.html?app=powerpoint"/>
      </bt:Urls>
      <bt:ShortStrings>
        <bt:String id="CommandsGroup.Label" DefaultValue="Supertext"/>
        <bt:String id="TaskpaneButton.Label" DefaultValue="Translate"/>
      </bt:ShortStrings>
      <bt:LongStrings>
      <bt:String id="TaskpaneButton.Tooltip" DefaultValue="Supertext Integration in Microsoft Office: Translate selected text or the whole document"/>
      </bt:LongStrings>
    </Resources>
      <!-- TODO: Change the ID in the <Id> and the <Resource> elements before distributing the manifest -->
    <WebApplicationInfo>
      <Id>dcfd3f9f-bc83-4c69-acd5-6675a31c413c</Id>
      <Resource>api://production.ai-office-add-in.supertext.com/dcfd3f9f-bc83-4c69-acd5-6675a31c413c</Resource>
      <Scopes>
        <Scope>profile</Scope>
        <Scope>openid</Scope>
      </Scopes>
    </WebApplicationInfo>
  </VersionOverrides>
</OfficeApp>