diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
 # Changelog for notion-client
 
+## 0.7.0.2 (2026-06-27)
+
+### Bug Fixes
+* Relation property schemas with `single_property` now serialize the required empty `single_property` object, so creating one-directional and self-referential relation columns no longer fails Notion validation with "is not a valid property schema"
+
 ## 0.7.0.1 (2026-04-16)
 
 ### Bug Fixes
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -147,6 +147,51 @@
         }
 ```
 
+## Usage with effectful
+
+Callers that use the [`effectful`](https://hackage.haskell.org/package/effectful)
+effect system can opt into an `Eff`-typed surface via the companion
+package
+[`notion-client-effectful`](./notion-client-effectful/). Every
+`Notion.V1.Methods` field is re-exposed as a smart constructor of a
+`Notion` effect, and a `runNotion` interpreter dispatches through a
+concrete `Methods` value. `NotionError` responses surface via the
+`Error NotionError` effect rather than as `IO` exceptions.
+
+```haskell
+module Demo where
+
+import Data.Text (Text)
+import Data.Text qualified as Text
+import Effectful (Eff, runEff, (:>))
+import Effectful.Error.Static (Error, runErrorNoCallStack)
+import Notion.V1                    (getClientEnv, makeMethods)
+import Notion.V1.Common             (UUID (..))
+import Notion.V1.Effectful qualified as NE
+import Notion.V1.Error              (NotionError)
+import System.Environment qualified as Env
+
+demo :: (NE.Notion :> es, Error NotionError :> es) => UUID -> Eff es Text
+demo pid = do
+  page <- NE.retrievePage pid
+  pure (Text.pack (show page))
+
+main :: IO ()
+main = do
+  token <- Text.pack <$> Env.getEnv "NOTION_TOKEN"
+  env <- getClientEnv "https://api.notion.com/v1"
+  let methods = makeMethods env token
+  result <-
+    runEff . runErrorNoCallStack @NotionError . NE.runNotion methods $
+      demo (UUID "00000000-0000-0000-0000-000000000000")
+  print result
+```
+
+See [`notion-client-effectful/README.md`](./notion-client-effectful/README.md)
+for the full import pattern (qualifying one of the two `Notion.V1`
+modules is required — every smart constructor shares its name with
+the matching `Methods` record selector).
+
 ## API Coverage
 
 - **Databases**: Create, retrieve, update, and query databases
diff --git a/notion-client.cabal b/notion-client.cabal
--- a/notion-client.cabal
+++ b/notion-client.cabal
@@ -1,6 +1,6 @@
 cabal-version:      3.4
 name:               notion-client
-version:            0.7.0.1
+version:            0.7.0.2
 synopsis:           Type-safe Haskell client for the Notion API
 description:
   This package provides comprehensive and type-safe bindings
diff --git a/src/Notion/V1/Properties.hs b/src/Notion/V1/Properties.hs
--- a/src/Notion/V1/Properties.hs
+++ b/src/Notion/V1/Properties.hs
@@ -499,7 +499,12 @@
   FormulaSchema {..} -> (schemaId, schemaName, "formula", object ["expression" .= formulaExpression])
   RelationSchema {..} ->
     let relObj = case relationType of
-          SingleProperty -> object ["data_source_id" .= relationDataSourceId, "type" .= ("single_property" :: Text)]
+          SingleProperty ->
+            object
+              [ "data_source_id" .= relationDataSourceId,
+                "type" .= ("single_property" :: Text),
+                "single_property" .= object []
+              ]
           DualProperty {..} ->
             object
               [ "data_source_id" .= relationDataSourceId,
diff --git a/tasty/Main.hs b/tasty/Main.hs
--- a/tasty/Main.hs
+++ b/tasty/Main.hs
@@ -660,6 +660,8 @@
       testCase "PropertySchema number round-trip" testPropertySchemaNumberRoundTrip,
       testCase "PropertySchema formula round-trip" testPropertySchemaFormulaRoundTrip,
       testCase "PropertySchema relation dual round-trip" testPropertySchemaRelationRoundTrip,
+      testCase "PropertySchema relation single shape" testPropertySchemaRelationSingleShape,
+      testCase "PropertySchema relation single round-trip" testPropertySchemaRelationSingleRoundTrip,
       testCase "PropertySchema status round-trip" testPropertySchemaStatusRoundTrip,
       testCase "NumberFormat round-trip" testNumberFormatRoundTrip,
       testCase "RollupFunction round-trip" testRollupFunctionRoundTrip,
@@ -2009,6 +2011,43 @@
       schema = Props.RelationSchema {schemaId = "r1", schemaName = "Tasks", relationDataSourceId = UUID "ds-123", relationType = relType}
       json = Aeson.toJSON schema
   case Aeson.fromJSON json of
+    Aeson.Success decoded -> assertEqual "round-trip" schema decoded
+    Aeson.Error err -> assertFailure $ "Failed to decode: " <> err
+
+testPropertySchemaRelationSingleShape :: Assertion
+testPropertySchemaRelationSingleShape = do
+  let schema =
+        Props.RelationSchema
+          { schemaId = "r1",
+            schemaName = "Depends On",
+            relationDataSourceId = UUID "ds-123",
+            relationType = Props.SingleProperty
+          }
+      json = Aeson.toJSON schema
+      expected =
+        Aeson.object
+          [ "id" Aeson..= ("r1" :: Text.Text),
+            "name" Aeson..= ("Depends On" :: Text.Text),
+            "type" Aeson..= ("relation" :: Text.Text),
+            "relation"
+              Aeson..= Aeson.object
+                [ "data_source_id" Aeson..= ("ds-123" :: Text.Text),
+                  "type" Aeson..= ("single_property" :: Text.Text),
+                  "single_property" Aeson..= Aeson.object []
+                ]
+          ]
+  assertEqual "single-property relation JSON shape" expected json
+
+testPropertySchemaRelationSingleRoundTrip :: Assertion
+testPropertySchemaRelationSingleRoundTrip = do
+  let schema =
+        Props.RelationSchema
+          { schemaId = "r1",
+            schemaName = "Depends On",
+            relationDataSourceId = UUID "ds-123",
+            relationType = Props.SingleProperty
+          }
+  case Aeson.fromJSON (Aeson.toJSON schema) of
     Aeson.Success decoded -> assertEqual "round-trip" schema decoded
     Aeson.Error err -> assertFailure $ "Failed to decode: " <> err