Get request not sending parameter via url to the api controller

I have this simple API controller in a NetCore 2.2 web game that is supposed to return a list of monsters based on the dungeonID(Guid).

So I use the URL, passing in the guid of the dungeonID, to that controller like this:

https://localhost:44361/MonsterList/GetMonsters/2f14c8gf-2e7e-466a-bcbg-f4440e92b3dg

But when I step through the code, I just see all zeroes for the dungeonID:

    public async Task<JsonResult> GetMonsters(Guid dungeonID)
    {
        var monsters = await _context.MonsterList.Where(c => c.DungeonID == (dungeonID)).ToListAsync();

        return Json(monsters);
    }

This returns nothing because, for reasons I don't know, dungeonID is always all zeroes.

But this does work if I hard-code in the dungeonID:

https://localhost:44361/MonsterList/GetMonsters

public async Task<JsonResult> GetMonsters()
{
    var monsters = await _context.MonsterList.Where(c => c.DungeonID == Guid.Parse("2f14c8gf-2e7e-466a-bcbg-f4440e92b3dg")).ToListAsync();

    return Json(monsters);
}

I've seen lots of posts similiar to mine, like these:

asp.net webapi 2 post parameter is always null

Post parameter is always null

But nothing seems to work.

How do I add the ability to pass in a Guid parameter?

Thanks!