Activating multiple selection mode for a button triggering a function

[alex-swiftify]

I have followed the steps in https://learn.microsoft.com/en-us/office/dev/add-ins/outlook/item-multi-select?tabs=xmlmanifest to activate the multiple selection mode for my add-in.

            <ExtensionPoint xsi:type="MessageReadCommandSurface">
              <OfficeTab id="TabDefault">
                <Group id="msgExplorerCmdGroup">
                  <Label resid="CommandGroup.Label"/>
                  <Control xsi:type="Button" id="SyncButton">
                    <Label resid="SyncButton.Label"/>
                    <Supertip>
                      <Title resid="SyncButton.ShortTooltip"/>
                      <Description resid="SyncButton.LongTooltip"/>
                    </Supertip>
                    <Icon>
                      <bt:Image size="16" resid="Sync.16x16"/>
                      <bt:Image size="32" resid="Sync.32x32"/>
                      <bt:Image size="80" resid="Sync.80x80"/>
                    </Icon>
                    <Action xsi:type="ExecuteFunction">
                      <FunctionName>onSyncButtonClicked</FunctionName>
                       <!-- Attempt to enable multi-select mode -->
                      <SupportsMultiSelect>true</SupportsMultiSelect>
                    </Action>
                  </Control>
                </Group>
              </OfficeTab>
            </ExtensionPoint>

However, I'm receiving a "please try again later" error when trying to sideload the add-in (in new Outlook for Mac).
Is SupportsMultiSelect mode unsupported for "ExecuteFunction" actions?
In other words, is there any way to have a toolbar button handle multiple selected messages without implementing a task pane?

[whoanuragverma]

SupportsMultiSelect is only supported for ShowTaskpane. As multiselect relies on SelectedItemsChanged event, you would have to implement a taskpane. You can read more about it here.

You can also check the scehma reference for xsi:type="ExecuteFunction"

[alex-swiftify]

@whoanuragverma Thank you very much for confirming.
That’s quite unfortunate for our needs, but now we know what the limitations are.

[whoanuragverma]

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