diff --git a/infrastructure/abri/abri_client.py b/infrastructure/abri/abri_client.py
index 19054d200..66e094eab 100644
--- a/infrastructure/abri/abri_client.py
+++ b/infrastructure/abri/abri_client.py
@@ -78,14 +78,21 @@ class AbriClient:
         return self._parse_job_logged(outcome)
 
     def amend_job(self, request: AmendJobRequest) -> AmendJobResult:
+        # OpenHousing silently drops the appointment unless a bookable resource
+        # is sent, so fall back to the configured surveyor when the request
+        # carries no explicit override (mirrors log_job).
+        resource = (
+            request.resource
+            if request.resource is not None
+            else self._config.default_resource
+        )
         parameters = [
             ("job_no", request.job_no),
             ("action", "amend"),
             ("appointment_date", _format_appointment_date(request.appointment_date)),
             ("appointment_time", request.appointment_time),
+            ("resource", resource),
         ]
-        if request.resource is not None:
-            parameters.append(("resource", request.resource))
 
         outcome = self._exchange(
             request_type="amendoptiappt",
diff --git a/infrastructure/abri/config.py b/infrastructure/abri/config.py
index f2da18a77..f29e3f10c 100644
--- a/infrastructure/abri/config.py
+++ b/infrastructure/abri/config.py
@@ -11,9 +11,16 @@ class AbriConfig:
 
     @classmethod
     def from_env(cls, env: Mapping[str, str]) -> "AbriConfig":
+        # A blank default_resource does not error at the relay — OpenHousing
+        # logs the job but silently drops the appointment — so reject it here
+        # rather than let the misconfiguration ship an empty resource.
+        default_resource = env["ABRI_RELAY_DEFAULT_RESOURCE"]
+        if not default_resource.strip():
+            raise ValueError("ABRI_RELAY_DEFAULT_RESOURCE must not be blank")
+
         return cls(
             endpoint_url=env["ABRI_RELAY_URL"],
             username=env["ABRI_RELAY_USERNAME"],
             password=env["ABRI_RELAY_PASSWORD"],
-            default_resource=env["ABRI_RELAY_DEFAULT_RESOURCE"],
+            default_resource=default_resource,
         )
diff --git a/tests/infrastructure/abri/test_abri_client.py b/tests/infrastructure/abri/test_abri_client.py
index e891e4283..42ede432a 100644
--- a/tests/infrastructure/abri/test_abri_client.py
+++ b/tests/infrastructure/abri/test_abri_client.py
@@ -410,10 +410,12 @@ def test_amend_job_sends_the_recorded_amendoptiappt_envelope_to_the_relay_endpoi
     )
 
 
-def test_amend_job_omits_the_resource_parameter_when_no_surveyor_is_provided(
+def test_amend_job_defaults_the_resource_to_the_configured_surveyor(
     client: AbriClient, mock_session: MagicMock
 ) -> None:
-    # Arrange
+    # Arrange: OpenHousing silently drops the appointment unless a bookable
+    # resource is sent, so an amend without an explicit surveyor falls back to
+    # the configured default rather than omitting the parameter.
     mock_session.post.return_value.content = _load_fixture(
         "abri_relay_amendoptiappt_success_response.xml"
     )
@@ -423,11 +425,12 @@ def test_amend_job_omits_the_resource_parameter_when_no_surveyor_is_provided(
 
     # Assert
     sent_body: bytes = mock_session.post.call_args.kwargs["data"]
-    sent_attributes = [
-        parameter.get("attribute")
+    resources = [
+        parameter.get("attribute_value")
         for parameter in ET.fromstring(sent_body).findall(".//Parameters")
+        if parameter.get("attribute") == "resource"
     ]
-    assert "resource" not in sent_attributes
+    assert resources == [CONFIG.default_resource]
 
 
 # --- amend_job: rejection ---
diff --git a/tests/infrastructure/abri/test_abri_config.py b/tests/infrastructure/abri/test_abri_config.py
index 4e1d8c87d..0884a14a3 100644
--- a/tests/infrastructure/abri/test_abri_config.py
+++ b/tests/infrastructure/abri/test_abri_config.py
@@ -1,3 +1,5 @@
+import pytest
+
 from infrastructure.abri.config import AbriConfig
 
 
@@ -20,3 +22,18 @@ def test_config_hydrates_relay_credentials_and_defaults_from_environment() -> No
         password="secret",
         default_resource="CBRYAN",
     )
+
+
+@pytest.mark.parametrize("blank", ["", "   "])
+def test_config_rejects_a_blank_default_resource(blank: str) -> None:
+    # A blank resource does not error at the relay: OpenHousing logs the job
+    # but silently drops the appointment. Fail loudly at config load instead.
+    env = {
+        "ABRI_RELAY_URL": "https://relay.example.test/api/DomnaRelay?code=key",
+        "ABRI_RELAY_USERNAME": "DomnaWeb",
+        "ABRI_RELAY_PASSWORD": "secret",
+        "ABRI_RELAY_DEFAULT_RESOURCE": blank,
+    }
+
+    with pytest.raises(ValueError, match="ABRI_RELAY_DEFAULT_RESOURCE"):
+        AbriConfig.from_env(env)
diff --git a/tests/orchestration/test_abri_orchestrator_amend_job.py b/tests/orchestration/test_abri_orchestrator_amend_job.py
index f5ba20e57..1a3386a5b 100644
--- a/tests/orchestration/test_abri_orchestrator_amend_job.py
+++ b/tests/orchestration/test_abri_orchestrator_amend_job.py
@@ -114,6 +114,9 @@ def test_amend_job_sends_an_amendoptiappt_envelope_for_the_deals_recorded_job(
         "action": "amend",
         "appointment_date": "24/06/2026",
         "appointment_time": "PM",
+        # OpenHousing drops the appointment without a bookable resource, so the
+        # amend defaults to the configured surveyor when none is overridden.
+        "resource": CONFIG.default_resource,
     }