diff --git a/packages/frontend-plugin-api/src/schema/createPortableSchema.test.ts b/packages/frontend-plugin-api/src/schema/createPortableSchema.test.ts
index d612578f32..7ea5943f17 100644
--- a/packages/frontend-plugin-api/src/schema/createPortableSchema.test.ts
+++ b/packages/frontend-plugin-api/src/schema/createPortableSchema.test.ts
@@ -349,5 +349,36 @@ describe('createConfigSchema', () => {
         additionalProperties: false,
       });
     });
+
+    it('should throw a clear error for non-object input', () => {
+      const schema = createConfigSchema({ title: z => z.string() });
+
+      expect(() => schema.parse('not an object')).toThrow(
+        'Invalid config input, expected object but got string',
+      );
+      expect(() => schema.parse(42)).toThrow(
+        'Invalid config input, expected object but got number',
+      );
+      expect(() => schema.parse([1, 2])).toThrow(
+        'Invalid config input, expected object but got array',
+      );
+      expect(() => schema.parse(true)).toThrow(
+        'Invalid config input, expected object but got boolean',
+      );
+    });
+
+    it('should not mark defaulted zod v3 fields as required in JSON Schema', () => {
+      const schema = createConfigSchema({
+        name: z => z.string(),
+        title: z => z.string().default('hello'),
+        count: z => z.number().optional(),
+      });
+
+      const result = schema.schema();
+      expect(result.schema).toMatchObject({
+        type: 'object',
+        required: ['name'],
+      });
+    });
   });
 });
diff --git a/packages/frontend-plugin-api/src/schema/createPortableSchema.ts b/packages/frontend-plugin-api/src/schema/createPortableSchema.ts
index 0abd3224fa..e1482475ef 100644
--- a/packages/frontend-plugin-api/src/schema/createPortableSchema.ts
+++ b/packages/frontend-plugin-api/src/schema/createPortableSchema.ts
@@ -100,6 +100,17 @@ function buildPortableSchema<TOutput = unknown>(
   fields: Record<string, ResolvedField>,
 ): MergeablePortableSchema<TOutput> {
   function parse(input: unknown) {
+    if (
+      input !== undefined &&
+      input !== null &&
+      (typeof input !== 'object' || Array.isArray(input))
+    ) {
+      throw new Error(
+        `Invalid config input, expected object but got ${
+          Array.isArray(input) ? 'array' : typeof input
+        }`,
+      );
+    }
     const inputObj = (input ?? {}) as Record<string, unknown>;
     const result: Record<string, unknown> = {};
     const errors: string[] = [];
diff --git a/packages/frontend-plugin-api/src/wiring/createExtension.ts b/packages/frontend-plugin-api/src/wiring/createExtension.ts
index 33f3bca158..d7d90079a2 100644
--- a/packages/frontend-plugin-api/src/wiring/createExtension.ts
+++ b/packages/frontend-plugin-api/src/wiring/createExtension.ts
@@ -726,18 +726,16 @@ export function createExtension(
         ),
         output: (overrideOptions.output ??
           options.output) as ExtensionDataRef[],
-        config:
+        configSchema:
           options.config ||
           options.configSchema ||
           overrideOptions.config ||
           overrideOptions.configSchema
             ? {
-                schema: {
-                  ...options.config?.schema,
-                  ...options.configSchema,
-                  ...overrideOptions.config?.schema,
-                  ...overrideOptions.configSchema,
-                },
+                ...options.config?.schema,
+                ...options.configSchema,
+                ...overrideOptions.config?.schema,
+                ...overrideOptions.configSchema,
               }
             : undefined,
         factory: ({ node, apis, config, inputs }) => {