No such host is known in Test and Production - iis

Question

In my .Net Core controller I have a "PublishDraft" action. This works as expected in localhost during development. Once this is deployed to the Test or Production servers, this action returns the "No such host is known" error.
This is one of many actions on this controller, and they all work in Test and Production except for this one single PublishDraft() action. So this tells me it cannot be a DNS issue since all the other actions work.
[HttpPost("PublishDraft")]
public async Task<IActionResult> PublishDraft([FromBody] PublishDraftRequest request)
{
try
{
var existing = _unitOfWork.Drafts.GetAll(d => d.Id == request.DraftId, null, "DraftTags").FirstOrDefault();
if (existing == null)
{
return NotFound("Draft does not exist");
}
var created = await _unitOfWork.Drafts.PublishDraft(existing, User.Claims.GetUserId());
if (created.TreeNodeTypeId == (int)TreeNodeTypes.Private && created.ParentId != null)
{
await _unitOfWork.TreeNodeUser.UpdateUserPermissionsAsync(created.Id, created.ParentId, User.Claims.GetUserId());
}
return Created("TreeNode", created);
}
catch (Exception ex)
{
logger.LogError(ex, User);
return BadRequest(ex.Message);
}
}
Whether I test this using the web client (Angular) or PostMan in Test or Production, I get the same error on this single action.
The servers are IIS 10.
Any ideas why this is happening?
UPDATE:
To answer questions from the commenters about what the exception call stack shows, there is no exception! The controller action is never hit, so no exception is logged.
UPDATE 2 - Added screenshots of error
Dev Tools Header screenshot
(I removed the domain name in this screenshot)
Dev Tools Response screenshot
I found an interesting anomaly that changes the way I look at this issue, I'm only getting the "unknown host" error when the DraftId exists. But when I pass in a bogus DraftId, then I get the error message "Draft does not exist", which tells me that the controller action is actually being hit after all.
I still don't know why the "unknown host" error occurs in Test or Production and it works locally in development, but I'm adding some trace logging to see if I can find out where the issue is occurring.
Solved - Sept. 9, 2021
It's simply a cause of not being consistent on my part. It all came down to a trailing slash on an endpoint.
(Sprinkling trace logs throughout my code helped me track down the cause.)
My service needs to use the HttpClient to call an external api from inside the PublishDraft() method of the controller action.
My localhost appSettings has a config for the base endpoint like this:
"EndPointsConfig": {
"FileStore": "https://localhost:44314/"
}
The trailing slash is correct.
My Testing and Production appSettings properties were:
"EndPointsConfig": {
"FileStore": "https://filestore.domain.com"
}
The missing trailing slash caused the "No such host is known" error, since it had to concat the path to a method and with no slash / it was clearly incorrect.
Like this: https://filestore.domain.com/deleterange
Once the slash was added, it all worked!
Hopefully others find this useful in solving similar issues.