ASP.NET Core Swagger error - Conflicting method/path combination

After adding a new method to a controller, my OpenAPI(Swagger) endpoint started to complain with the following error message:

Conflicting method/path combination "POST api/Orders" for actions - eShopExample.Web.Controllers.OrdersController.CreateOrder (eShopExample),eShopExample.Web.Controllers.OrdersController.ProcessOrders (eShopExample). Actions require a unique method/path combination for Swagger/OpenAPI 3.0. Use ConflictingActionsResolver as a workaround

I find the error message itself not very insightful but taking a look at my OrdersController made it all clear:

	public class OrderController: Controller
	{
	// POST api/order
	[HttpPost]
	[ProducesResponseType(StatusCodes.Status200OK)]
	[ProducesResponseType(StatusCodes.Status400BadRequest)]
	public async Task<ActionResult> CreateOrder(OrderProductCommand command)
	{
	var order = await _orderService.OrderProduct(command);
	await _publishEndpoint.Publish(new PlaceOrderMessage { OrderId = order.Id });
	return Ok();
	}
	[HttpPost]
	[ProducesResponseType(StatusCodes.Status200OK)]
	[ProducesResponseType(StatusCodes.Status400BadRequest)]
	public async Task<ActionResult> ProcessOrders(ICollection<Guid> orderIds)
	{
	var serviceClient = _busControl.CreateServiceClient();
	var requestClient = serviceClient.CreateRequestClient<ProcessOrdersJob>();
	var response = await requestClient.GetResponse<JobSubmissionAccepted>(new ProcessOrdersJob
	{
	JobId = Guid.NewGuid(),
	OrderIds = new List<Guid>(orderIds)
	});
	return Ok(response);
	}
	}

view raw OrderController.cs hosted with ❤ by GitHub

The problem was that I had 2 methods that were both using attribute based routing(through the [HttpPost] attribute) but where resolved to the same URI; “api/orders”. To fix it I had to use an overload of the [HttpPost] attribute and specify an alternative URI:

	[HttpPost("processorders")]
	[ProducesResponseType(StatusCodes.Status200OK)]
	[ProducesResponseType(StatusCodes.Status400BadRequest)]
	public async Task<ActionResult> ProcessOrders(ICollection<Guid> orderIds)
	{
	var serviceClient = _busControl.CreateServiceClient();
	var requestClient = serviceClient.CreateRequestClient<ProcessOrdersJob>();
	var response = await requestClient.GetResponse<JobSubmissionAccepted>(new ProcessOrdersJob
	{
	JobId = Guid.NewGuid(),
	OrderIds = new List<Guid>(orderIds)
	});
	return Ok(response);
	}

view raw ProcessOrdersFixed.cs hosted with ❤ by GitHub