1. Set Payload "Start"
2. 'Is Balnk String' Creates an Error object with #[error.description] ="String is not blank"
3. Default Error Handler catches and Propagates error
4. 'On Error Propogate' is 'RED IN RED OUT'. It Returns Status Code : 500 & #[error.description]
-------------------------------------------------------------------------------------------------------------------------- Correct answer is String is not blank. Because validation component will throw an error as payload is not blank.
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Response body: "Error" Default response status code: 200.
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1) Payload is successfully set to "Success - Started Flow"
2) When HTTP Request throws an error, execution halts
#[error.description] = "ABC"
#[error.errorType] = "XYZ"
3) The On Error Continue scope handles the error. When On Error Continue scope is invoked, all the processors in error block are executed and success response is sent back to the client with payload which is set in error flow. In this case payload is set to "Error" value in error block.
4) "Error" is returned to the requestor in the body of the HTTP request with HTTP Status Code: 200 as On error continue always sends success error code.
Reference Diagram:

* To use custom modules, you need to import the module or functions you want to use by adding the import directive to the head of your DataWeave script, for example:
1) Does not identify any functions to import from the String module:
import dw::core::Strings
2) To identify a specific function to import from the String module:
import camelize, capitalize from dw::core::Strings
3) To import all functions from the String module:
import * from dw::core::Strings
The way you import a module impacts the way you need to call its functions from a DataWeave script. If the directive does not list specific functions to import or use * from to import all functions from a function module, you need to specify the module when you call the function from your script.
* In given scenario, it's mentioned to import all of the WebStore.dwl
So correct answer is:

Correct answer is Publish the API to Anypoint Exchange
Anypoint Exchange makes this possible by making it discoverable in below ways
1) In private exchange for internal developers
2) In a public portal for external developers/clients
Here is diagram created by me to help you understand sequence: