403 -> 400

Author: prwhelan

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/transform/action/PreviewTransformAction.java

@@ -138,7 +138,7 @@ public void writeTo(StreamOutput out) throws IOException {
                     "Cannot send a _preview request with "
                         + TransformField.PREVIEW_AS_INDEX_REQUEST.getPreferredName()
                         + " to an outdated node. Please upgrade the node to 9.3.0+ and try again.",
-                    RestStatus.FORBIDDEN
+                    RestStatus.BAD_REQUEST
                 );
             }
         }

x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/transform/action/PreviewTransformActionRequestTests.java

@@ -102,7 +102,7 @@ public void testAsIndexRequestIsNotBackwardsCompatible() throws IOException {
                         ElasticsearchStatusException.class,
                         () -> copyWriteable(testInstance, getNamedWriteableRegistry(), instanceReader(), unsupportedVersion)
                     );
-                    assertThat(statusException.status(), equalTo(RestStatus.FORBIDDEN));
+                    assertThat(statusException.status(), equalTo(RestStatus.BAD_REQUEST));
                     assertThat(
                         statusException.getMessage(),
                         equalTo(