Asp.net core : Calling web api returns 500

I am new to asp.net core application.

I have an asp.net core application which uses repository pattern. It have an api controller named ApplicationsAPIController.

ApplicationsAPIController has a GetApplications method which return all applications.

I have app published to remote server. While calling GetApplications api from postman throws500 Internal Server Error with following HTML as response:

<h1 class="text-danger">Error.</h1><h2 class="text-danger">An error occurred while processing your request. </h2><h3>Development Mode</h3><p>
    Swapping to <strong>Development</strong> environment will display more detailed  information about the error that occurred.</p><p><strong>Development environment should not be enabled in deployed applications</strong>, as it can result in sensitive information from exceptions being displayed to end users. For local debugging, development environment can be enabled by setting the<strong>ASPNETCORE_ENVIRONMENT</strong> environment variable to<strong>Development</strong>, and restarting the application.</p>

Note: Above api is working perfectly in development enviroment (locally).

As per the error, i think i have to set up a staging or production environment. But i could not find any good and step by step document to setup. I have tried it many ways but failed.

Can anyone please help me out.