Call a lambda function from a websub service as a callback url

What will be the callback url to call the netlify function from a websub service?” or anything like that?

@sujoys10 If you are asking about your function endpoint, then it has the form /.netlify/functions/<functionName>

Where functions/someFunction.js would be the bundled deployed function:

These endpoints can be found in the Netlify dashboard under the functions section of the site by clicking on the function.