Multiple optional parameters web api attribute routing

Question

I am new to attribute routing, and I am not sure if this is even possible.

I have an attribute route, which works fine like this:

[HttpGet]
[Route("GetIssuesByFlag/{flag:int=3}")]
public IEnumerable<IssueDto> GetIssuesByFlag(int flag)

Now I want to add some extra optional parameters to narrow down my search, so I want to add 2 extra optional parameters.

What I have tried:

[HttpGet]
[Route("GetIssuesByFlag/{flag:int=3?}/{categoryId:int?}/{tagIds?}")]
public IEnumerable<IssueDto> GetIssuesByFlag(int flag , int? categoryId = null, int?[] tagIds = null)

This works fine if my call is /api/controller/1/2, but fails with 404 when it comes to /api/controller/1.

How can I achieve this?

Edit 1: Nkosi's answer below worked, however an extra modification was needed.

[HttpGet]
[Route("GetIssuesByFlag/{flag:int=3}/{tagIds?}/{categoryId:int?}")]
public IEnumerable<IssueDto> GetIssuesByFlag(int flag , List<int> tagIds, int? categoryId = null )

The list or array must be second as it is automatically null if no value is provided and cant be marked as optional with = null.

Answer 1

{flag:int=3?} is the problem. it is either optional {flag:int?} with the default value in the action or {flag:int=3}.

[HttpGet]
Route("GetIssuesByFlag/{flag:int=3}/{categoryId:int?}/{tagIds?}")]
public IEnumerable<IssueDto> GetIssuesByFlag(int flag , int? categoryId = null, int?[] tagIds = null)

You currently have 3 optional parameters. when you have just the 1 value routing table wont know which optional parameter you are referring to, hence the 404