---
title: "Install and Use NVIDIA PAIR — Troubleshooting"
canonical: "https://build.nvidia.com/spark/pair/troubleshooting.md"
---

## Troubleshooting

Start with the symptom and then inspect **Settings → Service**, the desktop
error surface, or the terminal interface's **Errors** tab for more detail.

| Symptom | Usual meaning | What to do |
| --- | --- | --- |
| PAIR remains on **Loading...** | A background service did not start correctly. | Wait one or two minutes, then inspect **Settings → Service** and restart the affected service. |
| A node is not discovered | mDNS is blocked or unavailable. | Confirm both nodes are on the same trusted local network, allow `5353/udp`, or add the node by IP address. |
| Pairing stalls or fails | The invitation expired, the PIN is incorrect, or port `14321` is blocked. | Start a new invitation, enter the new PIN, and confirm cluster ports are reachable. |
| Connection refused | Nothing is listening at that address. | Copy the current URL from **Endpoints** and confirm the PAIR service is running. |
| `403` from another machine | PAIR endpoints accept loopback traffic only. | Run PAIR on the machine hosting the client and use its local endpoint. |
| `502` with `no active node` | No node is eligible for the request. | Start a compatible engine and make the requested model available on at least one online node. |
| Persistent `404` on inference | No eligible node has the requested model. | Verify the exact model name and prepare it on at least one node. |
| `400` or `422` | The request is malformed. | Correct its JSON, route, model name, or required fields; malformed requests are not retried. |
| A response arrives but **Jobs** is empty | Another process owns the expected proxy port. | Check **Endpoints** and **Settings → Service**, then change the PAIR port or stop the conflicting process. |
| Requests do not use every GPU | PAIR routes each request to one eligible node. | Send independent requests and verify **Ran on** for each job. PAIR does not split one request across GPUs. |
| Desktop and terminal behavior conflicts | Both PAIR interfaces are running on one system. | Stop one interface and use only the desktop application or terminal interface. |