Issue of Swagger, Postman

Question

Issue of Swagger, Postman

Jonathan 65

Hi,

Further to

https://learn.microsoft.com/en-us/answers/questions/5750852/issue-to-the-deployed-app

How to check and ensure Swagger, Postman is functioning well? On the client, how to trigger that Swagger, Postman of the server?

0 comments

3 answers

Your answer

Answer 1

Jack Dang (WICLOUD CORPORATION) 18,145 Microsoft External Staff Moderator

Hi @Jonathan ,

The problem is a package version conflict. Swashbuckle.AspNetCore 10.1.1 needs Microsoft.OpenApi ≥ 2.4.1, but your project has 1.6.28.

To fix it:

Update Microsoft.OpenApi:

dotnet add package Microsoft.OpenApi --version 2.4.1

Clean and rebuild:

dotnet clean
dotnet build

Run the app and check Swagger:

http://<your-server-address>/swagger

Jonathan 65 Reputation points

2026-02-06T09:09:18.38+00:00

You can please enable your 1st reply on Feb-6 to be fine to be selected as the answer. iFormfile is the main way to also transfer the data between the client and server right? I not yet got that file (above) ever created well on the machine till now.
Jack Dang (WICLOUD CORPORATION) 18,145 Reputation points Microsoft External Staff Moderator

2026-02-06T09:14:34.4966667+00:00

Hi @Jonathan ,

I have enabled it. Feel free to interact with the system accordingly.

Answer 2

Jack Dang (WICLOUD CORPORATION) 18,145 Microsoft External Staff Moderator

Hi @Jonathan ,

Thanks for reaching out.

To make sure Swagger and Postman are working correctly with your deployed Web API, you can follow these steps:

Check Swagger
- Open a browser and go to http://<your-server-address>/swagger.
- You should see a list of your API endpoints in the interactive Swagger UI. This UI is generated by your API from its OpenAPI document. See the official docs on how Swagger/OpenAPI works with ASP.NET Core here: https://learn.microsoft.com/en-us/aspnet/core/tutorials/web-api-help-pages-using-swagger?view=aspnetcore-8.0
- From this UI you can expand an endpoint and use the Try it out button to send sample requests and inspect responses, which lets you confirm your API endpoints are responding as expected.
- If you want deeper details on how to add and configure Swagger/OpenAPI to your ASP.NET Core project, you can check out: https://learn.microsoft.com/en-us/aspnet/core/tutorials/getting-started-with-swashbuckle?view=aspnetcore-8.0
Check with an API client
- Open Postman and create a request to one of your API endpoints using the correct HTTP method (GET, POST, PUT, DELETE) and required headers/body content.
- Send the request and verify the response matches what you expect. This confirms your API can be accessed externally and is responding correctly.
- Even though the official Microsoft docs don’t have a Postman tutorial for every scenario, you can use the API’s OpenAPI/Swagger JSON file as a source for Postman (import the swagger.json URL into Postman to get a full collection of endpoints). The official OpenAPI specification support in ASP.NET Core lets tools like Postman and Swagger UI understand your API surface: https://learn.microsoft.com/en-us/aspnet/core/fundamentals/openapi/using-openapi-documents?view=aspnetcore-10.0
Common Things to Verify
- If your API is hosted as an IIS subsite, make sure your app is configured to use the correct path base.
- Ensure the Application Pool in IIS is started, running the correct .NET runtime, and has access to your deployed files.
- Check logs or console output if any requests fail. This helps you identify configuration or runtime errors.
- For general guidance on deploying ASP.NET Core Web APIs (including serving Swagger/OpenAPI in production), see the official publish guidance: https://learn.microsoft.com/en-us/aspnet/core/tutorials/publish-to-iis?view=aspnetcore-10.0

Hope this helps! If my answer was helpful - kindly follow the instructions here so others with the same problem can benefit as well.

Jonathan 65 Reputation points

2026-02-03T07:40:50.3333333+00:00

Thanks a lot. Do I choose

to add the code below?
Jack Dang (WICLOUD CORPORATION) 18,145 Reputation points Microsoft External Staff Moderator

2026-02-03T10:12:10.08+00:00
Hi @Jonathan ,

Regarding your question, no, you don’t need to add a new .cs file.

The code in your second image should be added directly into Program.cs, not in a new file created using Add New Item.

That code is startup configuration code. ASP.NET Core only reads it from Program.cs. If you put it in a separate file, Swagger will not work.

So please:

Open Program.cs

Add or merge the code there

Rebuild and run the app

After that, you can test Swagger at:

http://<your-server-address>/swagger
Jonathan 65 Reputation points

2026-02-05T02:55:37.1433333+00:00

How to resolve it below?
Jack Dang (WICLOUD CORPORATION) 18,145 Reputation points Microsoft External Staff Moderator

2026-02-05T09:59:13.73+00:00
Hi @Jonathan ,

Thanks for the details.

This error happens because AddOpenApi() and MapOpenApi() are not available in your project setup. Those APIs only exist when the new OpenAPI package for .NET 9+ is installed and used correctly.

Right now, your project does not have that support, so the compiler can’t find those methods.

Below is how you can fix it:

Use Swagger (Swashbuckle) instead, which works on .NET 6/7/8 and IIS.

Install the Swagger package:

dotnet add package Swashbuckle.AspNetCore

Update Program.cs like this:

var builder = WebApplication.CreateBuilder(args); builder.Services.AddEndpointsApiExplorer(); builder.Services.AddSwaggerGen(); var app = builder.Build(); if (app.Environment.IsDevelopment()) { app.UseSwagger(); app.UseSwaggerUI(); } app.MapGet("/", () => "Hello world!"); app.Run();

Rebuild and run:

dotnet build dotnet run

Open:

http://<your-server-address>/swagger
Jonathan 65 Reputation points

2026-02-05T10:07:22.1433333+00:00

I've done your given steps, and still have
Jack Dang (WICLOUD CORPORATION) 18,145 Reputation points Microsoft External Staff Moderator

2026-02-05T10:26:55.6833333+00:00

Hi @Jonathan ,
Can you check my reply again as I can see that you haven't updated Program.cs yet?
Jonathan 65 Reputation points

2026-02-06T02:19:22.1066667+00:00

Thanks a lot. Can you see one issue below?
Jonathan 65 Reputation points

2026-02-06T04:29:53.7066667+00:00

Thanks a lot. I also can run the project with the success. Was that iFormfile created or not?
Jonathan 65 Reputation points

2026-02-06T08:06:14.9266667+00:00

I will check the other things further. Thanks
Jack Dang (WICLOUD CORPORATION) 18,145 Reputation points Microsoft External Staff Moderator

2026-02-06T09:04:21.6233333+00:00

Hi @Jonathan ,

IFormFile is only created when a client uploads a file.

If no file is sent in the request, it will be null.

If my answer was helpful - kindly follow the instructions here so others with the same problem can benefit as well.
Jack Dang (WICLOUD CORPORATION) 18,145 Reputation points Microsoft External Staff Moderator

2026-02-06T09:22:40.76+00:00

Hi @Jonathan ,

IFormFile is only for sending a file from the client to the server. It is not saved anywhere by default.

When a file is uploaded, ASP.NET Core holds it in memory (or a temp location) only during the request.

If you want the file to exist on the machine, your code must save it explicitly, for example to a folder on disk or another storage location.

If you don’t write code to save it, the file will disappear after the request finishes, which is why you don’t see it on the server.

You can test this by uploading a file from Swagger or Postman and then saving it in your upload endpoint.

Answer 3

To ensure that Swagger and Postman are functioning well, you can follow these steps:

Swagger:
- Verify that your Swagger configuration is correctly set up in your application. Ensure that you are using the correct version of Swashbuckle for your .NET version.
- Check if the Swagger UI is accessible by navigating to the Swagger endpoint (usually /swagger or /swagger/index.html in your application).
- Test the API endpoints listed in Swagger to see if they return the expected responses.
- If you're using JWT authentication, ensure that you are correctly authorizing requests in the Swagger UI by clicking on the "Authorize" button and entering a valid token.
Postman:
- Open Postman and create a new request to the API endpoint you want to test.
- Set the request method (GET, POST, etc.) and enter the URL of the endpoint.
- If your API requires authentication, make sure to include the appropriate headers (e.g., Authorization header with the Bearer token).
- Send the request and check the response to ensure it matches the expected output.
- You can also use Postman to automate tests and check for various response codes and data formats.

By following these steps, you can confirm that both Swagger and Postman are functioning correctly with your API.

Share via

Issue of Swagger, Postman

3 answers

Your answer