diff --git a/docs/content/getting-started/perform-check.mdx b/docs/content/getting-started/perform-check.mdx
index 01fa3e9130..507a944799 100644
--- a/docs/content/getting-started/perform-check.mdx
+++ b/docs/content/getting-started/perform-check.mdx
@@ -163,7 +163,12 @@ To check whether user `user:anne` has relationship `reader` with object `documen
   ]}
 />
 
-The result's `allowed` field will return `true` if the relationship exists and `false` if the relationship does not exist.
+The result's `allowed` field will be:
+- `true` if the relationship exists.
+- `false` if the relation is defined in your model but no matching tuple exists.
+
+If the relation is *not defined* in your model, the API will return a `400 Bad Request` instead of `false`.
+
 
 ### 03. Calling Batch Check API