In outlook add-ins try to add the ItemSend Event handling trigger in the manifest file

    <Requirements>
      <bt:Sets DefaultMinVersion="1.3">
        <bt:Set Name="Mailbox"/>
      </bt:Sets>
    </Requirements>
    <Hosts>
      <Host xsi:type="MailHost">
        <DesktopFormFactor>

          <!-- Message Compose -->
          <ExtensionPoint xsi:type="MessageComposeCommandSurface">
            <OfficeTab id="TabDefault">
              <Group id="msgComposeCmdGroup">
                <Label resid="CommandsGroup.Label"/>
                <Control xsi:type="Button" id="msgComposeInsertGist">
                  <Label resid="TaskpaneButton.Label"/>
                  <Supertip>
                    <Title resid="TaskpaneButton.SupertipTitle"/>
                    <Description resid="TaskpaneButton.SupertipText"/>
                  </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="Taskpane.Url"/>
                  </Action>
                </Control>
              </Group>
            </OfficeTab>
          </ExtensionPoint>

          <!-- Appointment Organizer Command Surface -->
          <ExtensionPoint xsi:type="AppointmentOrganizerCommandSurface">
            <OfficeTab id="TabDefault">
              <Group id="apptOrganizerCmdGroup">
                <Label resid="CommandsGroup.Label"/>
                <Control xsi:type="Button" id="apptOrganizerInsertGist">
                  <Label resid="TaskpaneButton.Label"/>
                  <Supertip>
                    <Title resid="TaskpaneButton.SupertipTitle"/>
                    <Description resid="TaskpaneButton.SupertipText"/>
                  </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="Taskpane.Url"/>
                  </Action>
                </Control>
              </Group>
            </OfficeTab>
          </ExtensionPoint>
          
          <!-- ItemSend Event -->
          <ExtensionPoint xsi:type="Events">
            <Event Type="ItemSend" FunctionExecution="synchronous" FunctionName="itemSendHandler" />
          </ExtensionPoint>

        </DesktopFormFactor>
      </Host>
    </Hosts>
    <Resources>
      <bt:Images>
        <bt:Image id="Icon.16x16" DefaultValue="https://localhost:3000/assets/icon-16.png"/>
        <bt:Image id="Icon.32x32" DefaultValue="https://localhost:3000/assets/icon-32.png"/>
        <bt:Image id="Icon.80x80" DefaultValue="https://localhost:3000/assets/icon-80.png"/>
      </bt:Images>
      <bt:Urls>
        <bt:Url id="Taskpane.Url" DefaultValue="https://localhost:3000/taskpane.html"/>
      </bt:Urls>
      <bt:ShortStrings>
        <bt:String id="CommandsGroup.Label" DefaultValue="Contoso Add-in"/>
        <bt:String id="TaskpaneButton.Label" DefaultValue="Hello world"/>
        <bt:String id="TaskpaneButton.SupertipTitle" DefaultValue="Hello world"/>
      </bt:ShortStrings>
      <bt:LongStrings>
        <bt:String id="TaskpaneButton.SupertipText" DefaultValue="Open the Hello world add-in"/>
      </bt:LongStrings>
    </Resources>
  </VersionOverrides>
</OfficeApp>

In outlook add-ins try to add the ItemSend Event handling trigger in the manifest file ,but when i try to install manifest.xml not installing some error thrown

How to add the item send Event handler on my outlook add-ins

How to trigger this when click the save button , how to trigger the event on my commands.js file

Note : my add-ins developed by using javascript