It will be easier to understand if you look at the image:

I am coding using AWS Lambda in node.js.

exports.handler = async (event) => {

const payload = 'hello from lambda 1';

const params = {
    FunctionName: 'lambda2',
    InvocationType: 'Event',
    Payload: JSON.stringify(payload),
};

const LambdaPromise = (params) => lambda.invoke(params).promise();

const responseFromLambda2 = await LambdaPromise(params);

return responseFromLambda2; //this should return {StatusCode: 202, Payload: ''}
};

I tried referring to the code above, but it failed.

A lambda invokes B lambda. And B lambda invokes many C lambdas asynchronously.

How do I know that B lambda ends with C lambdas?

I can't do this so Lambda A doesn't know if lambda B did its job properly.