diff --git a/pairing.py b/pairing.py
index c2d923f..be7a6a4 100644
--- a/pairing.py
+++ b/pairing.py
@@ -179,20 +179,26 @@ async def pair_spire(
     connection lifecycle out of the orchestration so this is unit-testable
     with a fake client.
 
-    `relays` are the relays the spire uses for its *own* events
-    (kind-21000/30078) — typically the operator's public nostrrelay; supplied by
-    the API layer. `bunker_relay` (the relay baked into `bunker_url`, where the
-    spire reaches the bunker) defaults to `relays[0]`; `keystore_passphrase`
-    defaults to the lnbits bunker setting. Both injectable for tests.
+    `bunker_relay` / `keystore_passphrase` default to the lnbits bunker
+    settings; injectable for tests. `relays` are the relays the spire will
+    use for its *own* events (kind-21000/30078) — typically the operator's
+    nostrrelay; supplied by the API layer.
 
     Raises PairingError on any bunker failure; no state is persisted here
     (the API layer persists on success).
     """
+    relay = (
+        bunker_relay if bunker_relay is not None else settings.lnbits_nsec_bunker_url
+    )
     passphrase = (
         keystore_passphrase
         if keystore_passphrase is not None
         else settings.lnbits_nsec_bunker_keystore_passphrase
     )
+    if not relay:
+        raise PairingError(
+            "LNBITS_NSEC_BUNKER_URL is not set — cannot build a spire bunker connection"
+        )
     if not passphrase:
         raise PairingError(
             "LNBITS_NSEC_BUNKER_KEYSTORE_PASSPHRASE is not set — "
@@ -200,14 +206,6 @@ async def pair_spire(
         )
     if not relays:
         raise PairingError("at least one relay is required for the seed URL")
-    # The relay baked into `bunker_url` is where the *spire* (the remote ATM)
-    # reaches the bunker, so it must be a machine-reachable public URL — NOT
-    # `settings.lnbits_nsec_bunker_url`, which is how the co-located lnbits
-    # reaches the bunker (typically ws://127.0.0.1, unreachable from the ATM —
-    # the localhost-relay /pair gotcha bitspire flagged). Default to the spire's
-    # own event relay (the bunker lives on the same operator relay the spire
-    # publishes to); an explicit `bunker_relay` overrides for split-relay deploys.
-    relay = bunker_relay if bunker_relay else relays[0]
 
     key_name = spire_key_name(machine.id)
     client_name = f"spire-client-{machine.id}"
@@ -252,7 +250,9 @@ async def pair_spire(
     )
 
 
-async def revoke_spire(machine: Machine, *, admin_client: NsecBunkerAdminClient) -> int:
+async def revoke_spire(
+    machine: Machine, *, admin_client: NsecBunkerAdminClient
+) -> int:
     """Revoke a spire's bunker access (the "Revoke spire access" UX,
     aiolabs/spirekeeper#9/#12).
 
@@ -274,4 +274,6 @@ async def revoke_spire(machine: Machine, *, admin_client: NsecBunkerAdminClient)
     except NsecBunkerNotConfiguredError as exc:
         raise PairingError(f"nsecbunkerd is not configured: {exc}") from exc
     except NsecBunkerError as exc:
-        raise PairingError(f"bunker admin RPC failed during revoke: {exc}") from exc
+        raise PairingError(
+            f"bunker admin RPC failed during revoke: {exc}"
+        ) from exc
diff --git a/tests/test_pairing.py b/tests/test_pairing.py
index e3d2999..080f5f9 100644
--- a/tests/test_pairing.py
+++ b/tests/test_pairing.py
@@ -218,29 +218,17 @@ def test_malformed_token_raises():
         _pair(bunker)
 
 
-def test_bunker_relay_defaults_to_spire_event_relay():
-    """No explicit bunker_relay -> the relay baked into bunker_url is the spire's
-    own public event relay (relays[0]), NOT lnbits's internal bunker URL. This
-    is the localhost-relay /pair gotcha: a UI-minted seed (the form has no
-    bunker_relay field) must embed a machine-reachable relay, not ws://127.0.0.1.
-    An empty bunker_relay falls back to the same default."""
-    from urllib.parse import quote
-
-    for empty in (None, ""):
-        result = asyncio.run(
+def test_missing_relay_or_passphrase_raises():
+    with pytest.raises(PairingError, match="LNBITS_NSEC_BUNKER_URL"):
+        asyncio.run(
             pair_spire(
                 _machine(),
                 relays=_RELAYS,
-                admin_client=FakeBunker(token_secret="s"),  # pragma: allowlist secret
-                bunker_relay=empty,
+                admin_client=FakeBunker(),
+                bunker_relay="",
                 keystore_passphrase=_PASSPHRASE,
             )
         )
-        assert f"relay={quote(_RELAYS[0], safe='')}" in result.bunker_url
-        assert "127.0.0.1" not in result.bunker_url
-
-
-def test_missing_relay_or_passphrase_raises():
     with pytest.raises(PairingError, match="PASSPHRASE"):
         asyncio.run(
             pair_spire(