In outlook Item send event handler , click the send button error thrown while Message sending

In Outlook New message compose or Edit the outlook event ,send button click ,(By use The Item send event handler In outlook add-ins) , click the send button this error thrown

But I want this , when i click the send button that one is trigger on my outlook add-ins command.js file , it not trigger anything in this file , this error thrown

In outlook add-ins manifest.xml file use this code for item send event handler

 <ExtensionPoint xsi:type="Events">
        <Event Type="ItemSend" FunctionExecution="synchronous" FunctionName="validateSubjectAndCC" />
      </ExtensionPoint>``

this mentioned function name called on my command.js file ,but inside the function not trigger anything , it shown on outlook info bar error

Notes : My outlook add-ins developed by using javascript language

Any thoughts about this Please share me

Thanks In Advance

Most probably the OfficeJS runtime can't locate the function mentioned in the add-in's manifest file. Make sure the add-in is hosted within a URL mentioned in the manifest file. Also you may try to run the sample add-in available on GitHub.