How to Fix a Unity Relay Join Code Coming Back Empty on the Host

If your host gets a blank Relay join code to hand to friends, the most common reason is racing the allocation. Relay needs a completed allocation before it can mint a join code. Here is the correct order.

How to fix it

1. Await the allocation first

Call var allocation = await RelayService.Instance.CreateAllocationAsync(maxConnections) and only then await RelayService.Instance.GetJoinCodeAsync(allocation.AllocationId). The code is derived from the allocation, so the allocation must exist first.

2. Set relay data before StartHost

Feed the allocation into the transport with transport.SetRelayServerData(new RelayServerData(allocation, "dtls")) and call this before NetworkManager.Singleton.StartHost(), or the host binds to the wrong endpoint.

3. Surface allocation errors

Wrap the calls in try/catch for RelayServiceException. A failed sign-in to Unity Authentication or an expired token throws here and leaves the join code empty, which looks identical to a race.

Catching the ones you can't reproduce

The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.

Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.

This is where a tool like Bugnet earns its place. Its SDK captures every Unity error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.