Outlook Add-in Fails to Update via Office 365 Admin Center Despite Passing Validation and Working Locally

I'm trying to update my Outlook add-in through the Office 365 admin center. The plugin manifest file I'm using was successfully used several months ago, and I was able to update the add-in without any issues at that time. I've made some minor changes - mostly URLs - and now I'm getting an error when trying to update it.

I ran the manifest validation tool, and it reported no errors. I installed the add-in on my local machine in Outlook, and it works

Any idea what it could be?

On the UI, it shows:

"Upload failed. Please check the manifest file and try again."

In the browser dev tools, I see the following:

{   "appDetail": null,   "returnedWorkloads": null,   "errorMessage": "[\"Exception thrown when extracting the given manifest\"] Error Response : , Error Message : , Response Headers : {\r\n  \"X-Frame-Options\": [\r\n    \"SAMEORIGIN\"\r\n  ],\r\n  \"X-DEPLOYMENT-ID\": [\r\n    \"2e22ae46-59b7-4232-8d99-2459ed635a6c\"\r\n  ],\r\n  \"x-ms-correlation-id\": [\r\n    \"52e082a7-c0de-4c6c-a89f-c51842e47d2e\"\r\n  ],\r\n  \"X-Content-Type-Options\": [\r\n    \"nosniff\"\r\n  ],\r\n  \"X-UA-Compatible\": [\r\n    \"IE=Edge\"\r\n  ],\r\n  \"X-Cache\": [\r\n    \"CONFIG_NOCACHE\"\r\n  ],\r\n  \"X-MSEdge-Ref\": [\r\n    \"Ref A: 63A102129DD042DC822B02D43B474F36 Ref B: BL2AA2030108007 Ref C: 2025-07-30T15:04:53Z\"\r\n  ]\r\n}",   "statusCode": "WxpoFailureError",   "statusCodeCategory": "WXPO" }

Manifest file:

<?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:mailappor="http://schemas.microsoft.com/office/mailappversionoverrides/1.0" xsi:type="MailApp">
    <Id>c6a9e8cd-239f-49c8-add4-2abd293b93ba</Id>
    <Version>1.0.5.0</Version>
    <ProviderName>Provider</ProviderName>
    <DefaultLocale>en-US</DefaultLocale>
    <DisplayName DefaultValue="[DEV] name"/>
    <Description DefaultValue="description"/>
    <IconUrl DefaultValue="https://HOST.com/assets/media/icon-64.png"/>
    <HighResolutionIconUrl DefaultValue="https://HOST.com/assets/media/icon-128.png"/>
    <SupportUrl DefaultValue="https://HOST.com"/>
    <AppDomains>
        <AppDomain>https://HOST.com</AppDomain>
    </AppDomains>
    <Hosts>
        <Host Name="Mailbox"/>
    </Hosts>

    <Requirements>
        <Sets>
            <Set Name="Mailbox" MinVersion="1.1"/>
        </Sets>
    </Requirements>

    <FormSettings>
        <Form xsi:type="ItemRead">
            <DesktopSettings>
                <SourceLocation DefaultValue="https://HOST.com/index.html"/>
                <RequestedHeight>250</RequestedHeight>
            </DesktopSettings>
        </Form>
    </FormSettings>

    <Permissions>ReadWriteItem</Permissions>

    <Rule xsi:type="RuleCollection" Mode="Or">
        <Rule xsi:type="ItemIs" ItemType="Message" FormType="Read"/>
    </Rule>

    <VersionOverrides xmlns="http://schemas.microsoft.com/office/mailappversionoverrides" xsi:type="VersionOverridesV1_0">
        <VersionOverrides xmlns="http://schemas.microsoft.com/office/mailappversionoverrides/1.1" xsi:type="VersionOverridesV1_1">
            <Requirements>
                <bt:Sets DefaultMinVersion="1.3">
                    <bt:Set Name="Mailbox"/>
                </bt:Sets>
            </Requirements>

            <Hosts>
                <Host xsi:type="MailHost">

                    <DesktopFormFactor>
                        <SupportsSharedFolders>true</SupportsSharedFolders>
          
                        <ExtensionPoint xsi:type="AppointmentOrganizerCommandSurface">
                            <OfficeTab id="TabDefault">
                                <Group id="msgComposeGroup">
                                    <Label resid="GroupLabel"/>
         

                                    <Control xsi:type="Button" id="msgComposeOpenPaneButton">
                                        <Label resid="OfficeTaskpaneBtn.Label"/>
                                        <Supertip>
                                            <Title resid="OfficeTaskpaneBtn.Label"/>
                                            <Description resid="OfficeTaskpaneBtn.Tooltip"/>
                                        </Supertip>
                                        <Icon>
                                            <bt:Image size="16" resid="Icon.16x16"/>
                                            <bt:Image size="32" resid="Icon.32x32"/>
                                            <bt:Image size="80" resid="Icon.80x80"/>
                                        </Icon>
                                        <Action xsi:type="ShowTaskpane">
                                            <SourceLocation resid="OfficeTaskpane.Url"/>
                                        </Action>
                                    </Control>
                                </Group>
                            </OfficeTab>
                        </ExtensionPoint>

                    </DesktopFormFactor>
                </Host>
            </Hosts>

            <Resources>
                <bt:Images>
                    <bt:Image id="Icon.16x16" DefaultValue="https://HOST.com/assets/media/icon-16.png"/>
                    <bt:Image id="Icon.32x32" DefaultValue="https://HOST.com/assets/media/icon-32.png"/>
                    <bt:Image id="Icon.80x80" DefaultValue="https://HOST.com/assets/media/icon-80.png"/>
                </bt:Images>
                <bt:Urls>
                    <bt:Url id="OfficeTaskpane.Url" DefaultValue="https://HOST.com/index.html?view=Grid"/>
                </bt:Urls>
                <bt:ShortStrings>
                    <bt:String id="GroupLabel" DefaultValue="$TEXT$"/>
                    <bt:String id="OfficeTaskpaneBtn.Label" DefaultValue="$TEXT$"/>
                </bt:ShortStrings>
                <bt:LongStrings>
                    <bt:String id="OfficeTaskpaneBtn.Tooltip" DefaultValue="$TEXT$"/>
                </bt:LongStrings>
            </Resources>

        </VersionOverrides>
    </VersionOverrides>
</OfficeApp>