diff --git a/src/lib/serviceRoutines/getEntities.c b/src/lib/serviceRoutines/getEntities.c
index fe75482b..90e07c26 100644
--- a/src/lib/serviceRoutines/getEntities.c
+++ b/src/lib/serviceRoutines/getEntities.c
@@ -1629,7 +1629,7 @@ bool getEntities(void)
     }
     if (corNgsild.orderGeometry != NULL && strcmp(corNgsild.orderGeometry, "Point") != 0)
     {
-      ldError(501, LD_ERROR_OP_NOT_SUPPORTED, "Not Implemented",
+      ldError(422, LD_ERROR_OP_NOT_SUPPORTED, "Operation Not Supported",
               "sort by distance is only supported for a Point orderGeometry (got '%s')", corNgsild.orderGeometry);
       return true;
     }
diff --git a/src/lib/serviceRoutines/getEntitiesTemporal.c b/src/lib/serviceRoutines/getEntitiesTemporal.c
index 77355c4f..2d8d0c1e 100644
--- a/src/lib/serviceRoutines/getEntitiesTemporal.c
+++ b/src/lib/serviceRoutines/getEntitiesTemporal.c
@@ -579,7 +579,7 @@ bool getEntitiesTemporal(void)
     //
     if (filter.qSqlPredicate == NULL)
     {
-      ldError(501, LD_ERROR_OP_NOT_SUPPORTED, "Operation Not Supported",
+      ldError(422, LD_ERROR_OP_NOT_SUPPORTED, "Operation Not Supported",
               "this 'q' cannot be evaluated against the temporal store");
       return true;
     }
diff --git a/src/lib/troe/troeNotAvailable.c b/src/lib/troe/troeNotAvailable.c
index 49dc4a4a..6846ccee 100644
--- a/src/lib/troe/troeNotAvailable.c
+++ b/src/lib/troe/troeNotAvailable.c
@@ -22,16 +22,21 @@ void troeNotAvailable(const char* op)
   // Two flavors:
   //  - no TRoE wired in at all (alias is NULL or "none") → "started without TRoE support"
   //  - a real plugin is active but doesn't implement this op → "plugin doesn't support op"
-  // 501 in either case: from the client's view the operation is not implemented
-  // by this server build/configuration.
+  // 422 in either case. From the client's view this IS "not implemented by this
+  // build", which reads like 501 - but TS 104-176 § 6.3.2 maps each error type to
+  // one status, and OperationNotSupported is 422. The only 501 in that table is
+  // NoMultiTenantSupport, a type reserved for one specific capability, so there
+  // is nothing registered that says "this deployment lacks an optional
+  // component" in general. See spec-doubts-2 #124; until it moves, the detail
+  // carries what the status cannot.
   if (strcmp(alias, "none") == 0)
   {
-    ldError(501, LD_ERROR_OP_NOT_SUPPORTED, "TRoE Not Available",
+    ldError(422, LD_ERROR_OP_NOT_SUPPORTED, "TRoE Not Available",
             "broker started without TRoE support; '%s' requires a TRoE plugin", op);
   }
   else
   {
-    ldError(501, LD_ERROR_OP_NOT_SUPPORTED, "TRoE Not Available",
+    ldError(422, LD_ERROR_OP_NOT_SUPPORTED, "TRoE Not Available",
             "TRoE plugin '%s' does not implement '%s'", alias, op);
   }
 }
diff --git a/test/funcTests/cases/geo_orderby_distance.test b/test/funcTests/cases/geo_orderby_distance.test
index 0aa2361a..a9641e4d 100644
--- a/test/funcTests/cases/geo_orderby_distance.test
+++ b/test/funcTests/cases/geo_orderby_distance.test
@@ -289,15 +289,15 @@ Content-Length: 189
 
 07. dist-asc with a non-Point orderGeometry — 501 Not Implemented
 =================================================================
-HTTP/1.1 501 Not Implemented
+HTTP/1.1 422 Unprocessable Content
 Date: REGEX(.*)
 Content-Type: application/json
-Content-Length: 216
+Content-Length: 224
 
 {
   "detail": "sort by distance is only supported for a Point orderGeometry (got 'LineString')",
-  "status": 501,
-  "title": "Not Implemented",
+  "status": 422,
+  "title": "Operation Not Supported",
   "type": "https://uri.etsi.org/ngsi-ld/errors/OperationNotSupported"
 }
 
diff --git a/test/funcTests/cases/geo_orderby_distance_corDB.test b/test/funcTests/cases/geo_orderby_distance_corDB.test
index 3aba46f1..b4bf9f28 100644
--- a/test/funcTests/cases/geo_orderby_distance_corDB.test
+++ b/test/funcTests/cases/geo_orderby_distance_corDB.test
@@ -285,15 +285,15 @@ Content-Length: 189
 
 07. dist-asc with a non-Point orderGeometry — 501 Not Implemented
 =================================================================
-HTTP/1.1 501 Not Implemented
+HTTP/1.1 422 Unprocessable Content
 Date: REGEX(.*)
 Content-Type: application/json
-Content-Length: 216
+Content-Length: 224
 
 {
   "detail": "sort by distance is only supported for a Point orderGeometry (got 'LineString')",
-  "status": 501,
-  "title": "Not Implemented",
+  "status": 422,
+  "title": "Operation Not Supported",
   "type": "https://uri.etsi.org/ngsi-ld/errors/OperationNotSupported"
 }
 
diff --git a/test/funcTests/cases/local_param_distops_suppress.test b/test/funcTests/cases/local_param_distops_suppress.test
index f2696804..6ff2406c 100644
--- a/test/funcTests/cases/local_param_distops_suppress.test
+++ b/test/funcTests/cases/local_param_distops_suppress.test
@@ -204,14 +204,14 @@ Content-Length: 152
 
 08. GET /temporal/entities/urn:S1 — accepted (plugin layer 501 is fine)
 =======================================================================
-HTTP/1.1 501 Not Implemented
+HTTP/1.1 422 Unprocessable Content
 Date: REGEX(.*)
 Content-Type: application/json
 Content-Length: REGEX(\d+)
 
 {
   "detail": "TRoE plugin 'ramdb' does not implement 'temporal-entity retrieve'",
-  "status": 501,
+  "status": 422,
   "title": "TRoE Not Available",
   "type": "https://uri.etsi.org/ngsi-ld/errors/OperationNotSupported"
 }
@@ -220,14 +220,14 @@ Content-Length: REGEX(\d+)
 
 09. GET /temporal/entities/urn:S1?local=true — accepted at API surface (regression: was 400)
 =============================================================================================
-HTTP/1.1 501 Not Implemented
+HTTP/1.1 422 Unprocessable Content
 Date: REGEX(.*)
 Content-Type: application/json
 Content-Length: REGEX(\d+)
 
 {
   "detail": "TRoE plugin 'ramdb' does not implement 'temporal-entity retrieve'",
-  "status": 501,
+  "status": 422,
   "title": "TRoE Not Available",
   "type": "https://uri.etsi.org/ngsi-ld/errors/OperationNotSupported"
 }
diff --git a/test/funcTests/cases/temporal_create_errors.test b/test/funcTests/cases/temporal_create_errors.test
index 99a2d1a0..082b99d1 100644
--- a/test/funcTests/cases/temporal_create_errors.test
+++ b/test/funcTests/cases/temporal_create_errors.test
@@ -138,14 +138,14 @@ Content-Length: 182
 
 04. valid URI but no TRoE plugin → 501 Not Implemented
 =======================================================
-HTTP/1.1 501 Not Implemented
+HTTP/1.1 422 Unprocessable Content
 Date: REGEX(.*)
 Content-Type: application/json
 Content-Length: 224
 
 {
   "detail": "broker started without TRoE support; 'temporal-entity create' requires a TRoE plugin",
-  "status": 501,
+  "status": 422,
   "title": "TRoE Not Available",
   "type": "https://uri.etsi.org/ngsi-ld/errors/OperationNotSupported"
 }
diff --git a/test/funcTests/cases/troe_disabled_temporal_501.test b/test/funcTests/cases/troe_disabled_temporal_not_supported.test
similarity index 69%
rename from test/funcTests/cases/troe_disabled_temporal_501.test
rename to test/funcTests/cases/troe_disabled_temporal_not_supported.test
index 83c1f6c5..3873c6b6 100644
--- a/test/funcTests/cases/troe_disabled_temporal_501.test
+++ b/test/funcTests/cases/troe_disabled_temporal_not_supported.test
@@ -1,16 +1,16 @@
 #
-# FILE            troe_disabled_temporal_501.test
+# FILE            troe_disabled_temporal_not_supported.test
 #
 # AUTHOR          Ken Zangelin
 #
 # Copyright 2026 Seamware
 #
 # § 6.18 — a broker started without TRoE support has no temporal storage; a
-# temporal-entity retrieve must be refused with 501 (Operation Not Supported),
+# temporal-entity retrieve must be refused with 422 (Operation Not Supported),
 # not attempted. The broker here runs with the default TRoE (none).
 #
 --NAME--
-GET /temporal/entities with TRoE disabled → 501 Operation Not Supported
+GET /temporal/entities with TRoE disabled → 422 Operation Not Supported
 
 --TAGS--
 troe temporal
@@ -21,7 +21,7 @@ coraineStart
 
 --RUN--
 
-echo "01. GET /temporal/entities/{id} — 501 (no TRoE backend)"
+echo "01. GET /temporal/entities/{id} — 422 (no TRoE backend)"
 echo "======================================================="
 corCurl --url /ngsi-ld/v1/temporal/entities/urn:ngsi-ld:T:1
 echo
@@ -29,16 +29,16 @@ echo
 
 
 --EXPECT--
-01. GET /temporal/entities/{id} — 501 (no TRoE backend)
+01. GET /temporal/entities/{id} — 422 (no TRoE backend)
 =======================================================
-HTTP/1.1 501 Not Implemented
+HTTP/1.1 422 Unprocessable Content
 Date: REGEX(.*)
 Content-Type: application/json
 Content-Length: 226
 
 {
   "detail": "broker started without TRoE support; 'temporal-entity retrieve' requires a TRoE plugin",
-  "status": 501,
+  "status": 422,
   "title": "TRoE Not Available",
   "type": "https://uri.etsi.org/ngsi-ld/errors/OperationNotSupported"
 }