Hi all, I have created a Web API exposing start process smart service

Please verify if you are authenticating while calling your Web API from browser. You need to use HTTP Basic Authentication

Also, are there any parameters that your process model takes? also since you are starting the process model, it will not be a GET request. It will be a POST request. Just entering the URL in browser will not be the right way to test it. You can use a browser extension like "Postman" to test your web api using the method POST, and also provide basic authentication.

As the above user suggested, you definitely have a Basic Auth problem. I would recommend you switch to something a bit more modern like Postman for testing purposes, it generates Basic Auth user / password really easily.

@bhargavie, Also please check the section:
https://forum.appian.com/suite/help/16.2/Web_APIs.html#HTTP_Status_Codes

The 500 status code may be related as per the below table.
404\tThere is no Web API with the specified endpoint and HTTP method
404\tThe user is not in the viewer role or higher for the Web API
500\tThere was an error evaluating the Web API's expression
500\tThe result of the expression evaluation was not an HTTP Response object.
Hope this helps.

@bhargavie - As @chetany suggested if you use any smart service in web API, then it cannot be executed just using URL with appended parameters to it. Post method must be used to access it. One of the option to test can be using a!httpwrite() function and calling the web API From there.

Hi,

I have a similar use-case, I want to start a process in Appian via an Email sent to a user.

Eg: An Email or attachment is sent to a user from Appian, he will click on it and a process instance has to be initiated in Appian.
I have created a Web API (method: POST) exposing start process smart service.

Added Viewer rights as well for the user.
How shall I configure Authentication in this case?

An API test tool, such as SoapUI, works nicely to test Appian web API calls.
The product doesn't currently support calling an Appian web api from the browser address bar alone.