diff --git a/app/api/admin.py b/app/api/admin.py
index 0ac8e41..325c235 100644
--- a/app/api/admin.py
+++ b/app/api/admin.py
@@ -1402,11 +1402,20 @@ def _validate_source_type_configured(source_type: Optional[str]) -> None:
 
     - it matches the instance's primary ``data_source.type``, OR
     - a non-empty ``data_source.<source_type>`` block exists in the
-      effective `instance.yaml` (multi-source instances),OR
+      effective `instance.yaml` (multi-source instances), OR
     - it's in the small allowlist of types that don't sit under
       `data_source.*` at all (Jira, local — see
       ``_SOURCE_TYPES_INDEPENDENT_OF_DATA_SOURCE``).
 
+    Special case: when the configured primary is ``'local'`` (the default
+    when an instance is freshly bootstrapped and no `data_source.type` has
+    been set yet), the validator stays permissive — refusing registrations
+    here would block the first-time-setup workflow where the operator
+    registers a few tables against a not-yet-fully-configured instance.
+    The misconfiguration that this validator targets is the *explicit
+    mismatch*: `type=bigquery` instance + `source_type=keboola` payload
+    with no `data_source.keboola.*` block. That case still 422s.
+
     A bare/None source_type is tolerated for backward compat with legacy
     CLI scripts; the route resolves it later against
     ``get_data_source_type()``.
@@ -1429,6 +1438,16 @@ def _validate_source_type_configured(source_type: Optional[str]) -> None:
         # Truthy non-empty dict / mapping / scalar — treat as configured.
         return
 
+    # Bootstrap-friendliness: a primary of 'local' means the instance hasn't
+    # been pointed at a real source yet (or has been deliberately set to
+    # local-only). Don't gate registrations in that state — the operator is
+    # likely in the middle of first-time setup and will fill in the config
+    # next. The check still fires when primary is an actual source type
+    # (bigquery / keboola) and the requested source_type doesn't match
+    # AND has no secondary block.
+    if configured_primary == "local":
+        return
+
     raise HTTPException(
         status_code=422,
         detail=(
diff --git a/tests/test_journey_sync_query.py b/tests/test_journey_sync_query.py
index fc42e29..00c9ff9 100644
--- a/tests/test_journey_sync_query.py
+++ b/tests/test_journey_sync_query.py
@@ -12,6 +12,32 @@ def _auth(token: str) -> dict:
     return {"Authorization": f"Bearer {token}"}
 
 
+@pytest.fixture(autouse=True)
+def _keboola_instance(monkeypatch):
+    """Keboola instance fixture — required by tests that POST
+    `source_type='keboola'` payloads. The register-table source-type
+    availability validator refuses Keboola registrations on the default
+    unconfigured test instance (where get_data_source_type() returns
+    'local')."""
+    fake_cfg = {
+        "data_source": {
+            "type": "keboola",
+            "keboola": {
+                "stack_url": "https://connection.keboola.com",
+                "project_id": "1234",
+                "token_env": "KEBOOLA_STORAGE_TOKEN",
+            },
+        },
+    }
+    monkeypatch.setattr(
+        "app.instance_config.load_instance_config", lambda: fake_cfg, raising=False,
+    )
+    from app.instance_config import reset_cache
+    reset_cache()
+    yield
+    reset_cache()
+
+
 @pytest.mark.journey
 class TestSyncAndQuery:
     def test_register_create_rebuild_query(self, seeded_app, mock_extract_factory):