Update custom operations documentation with supported argument examples

src/pages/[platform]/build-a-backend/data/custom-business-logic/index.mdx

@@ -510,6 +510,40 @@ safePrint(echoResponse.echo.content);
 ```
 
 </InlineFilter>
+## Supported Argument Types in Custom Operations
+
+Custom operations can accept different types of arguments. Understanding these options helps define flexible and well-structured APIs.
+
+### Defining Arguments in Custom Operations
+
+When defining a custom operation, you can specify arguments using different types:
+
+- **Scalar Fields**: Basic types such as `string`, `integer`, `float`, etc.
+- **Custom Types**: Define inline `customType`.
+- **Reference Types**: Use `a.ref()` to reference enums and custom types.
+
+```ts title="amplify/data/resource.ts"
+const schema = a.schema({
+  Status: a.enum({
+    values: ['ACCEPTED', 'REJECTED']
+  }),
+
+  echo: a
+    .query()
+    .arguments({
+      // scalar field
+      content: a.string(),
+      // inline custom type
+      config: a.customType({
+        filter: a.string(),
+        // reference to enum
+        status: a.ref('Status')
+      }),
+    })
+    .returns(a.string())
+    .authorization(allow => [allow.authenticated()])
+});
+```
 
 ## Async function handlers