diff --git a/src/api-client/api-client.test.ts b/src/api-client/api-client.test.ts
index 5d6d0fba..56565523 100644
--- a/src/api-client/api-client.test.ts
+++ b/src/api-client/api-client.test.ts
@@ -1188,7 +1188,30 @@ describe.skipIf(isLiveMode)('APIClient core', () => {
       expect(await client.getPlatformConfig(1)).toBeDefined();
 
       server.use(http.put(`${BASE_URL}/configs/1`, () => HttpResponse.json({ config: { id: 1 } })));
-      await client.updatePlatformConfig(1, { key: 'val' });
+      await client.updatePlatformConfig(1, { name: 'cfg', value: 'val' });
+    });
+
+    it('should PUT the full config object under data, not the bare value', async () => {
+      let sentBody: Record<string, unknown> = {};
+      server.use(
+        http.put(`${BASE_URL}/configs/22`, async ({ request }) => {
+          sentBody = (await request.json()) as Record<string, unknown>;
+          return HttpResponse.json({
+            ok: true,
+            config: { id: 22, name: 'experiment_form_max_secondary_metrics', value: '30' },
+          });
+        })
+      );
+
+      await client.updatePlatformConfig(22, {
+        name: 'experiment_form_max_secondary_metrics',
+        value: '30',
+      });
+
+      // Wire body must be {data: {name, value}} — not {data: '30'} or {data: {data: ...}}
+      expect(sentBody).toEqual({
+        data: { name: 'experiment_form_max_secondary_metrics', value: '30' },
+      });
     });
   });
 
diff --git a/src/commands/platformconfig/index.ts b/src/commands/platformconfig/index.ts
index a2e01ec3..ba670c1c 100644
--- a/src/commands/platformconfig/index.ts
+++ b/src/commands/platformconfig/index.ts
@@ -46,7 +46,7 @@ const updateCommand = new Command('update')
     withErrorHandling(async (id: number, options) => {
       const globalOptions = getGlobalOptions(updateCommand);
       const client = await getAPIClientFromOptions(globalOptions);
-      const value = validateJSON(options.value, '--value') as Record<string, unknown>;
+      const value = validateJSON(options.value, '--value');
       const result = await updatePlatformConfig(client, { id, value });
       console.log(chalk.green(`✓ Platform config ${id} updated`));
       printFormatted(result.data, globalOptions);
diff --git a/src/commands/platformconfig/platformconfig.test.ts b/src/commands/platformconfig/platformconfig.test.ts
index 5a722710..2a0b5b1e 100644
--- a/src/commands/platformconfig/platformconfig.test.ts
+++ b/src/commands/platformconfig/platformconfig.test.ts
@@ -23,9 +23,9 @@ describe('platform-config command', () => {
   let processExitSpy: ReturnType<typeof vi.spyOn>;
 
   const mockClient = {
-    listPlatformConfigs: vi.fn().mockResolvedValue([{ id: 1, value: 'test' }]),
-    getPlatformConfig: vi.fn().mockResolvedValue({ id: 1, value: 'test' }),
-    updatePlatformConfig: vi.fn().mockResolvedValue({ id: 1, value: 'new' }),
+    listPlatformConfigs: vi.fn().mockResolvedValue([{ id: 1, name: 'cfg', value: 'test' }]),
+    getPlatformConfig: vi.fn().mockResolvedValue({ id: 1, name: 'cfg', value: 'test' }),
+    updatePlatformConfig: vi.fn().mockResolvedValue({ id: 1, name: 'cfg', value: 'new' }),
   };
 
   beforeEach(() => {
@@ -61,7 +61,26 @@ describe('platform-config command', () => {
     expect(printFormatted).toHaveBeenCalled();
   });
 
-  it('should update platform config', async () => {
+  it('should fetch the current config and PUT the merged payload (string value)', async () => {
+    await platformConfigCommand.parseAsync(['node', 'test', 'update', '1', '--value', '"30"']);
+
+    expect(mockClient.getPlatformConfig).toHaveBeenCalledWith(1);
+    expect(mockClient.updatePlatformConfig).toHaveBeenCalledWith(1, {
+      name: 'cfg',
+      value: '30',
+    });
+  });
+
+  it('should accept a numeric value via --value', async () => {
+    await platformConfigCommand.parseAsync(['node', 'test', 'update', '1', '--value', '42']);
+
+    expect(mockClient.updatePlatformConfig).toHaveBeenCalledWith(1, {
+      name: 'cfg',
+      value: 42,
+    });
+  });
+
+  it('should accept an object as --value', async () => {
     await platformConfigCommand.parseAsync([
       'node',
       'test',
@@ -71,6 +90,9 @@ describe('platform-config command', () => {
       '{"key":"val"}',
     ]);
 
-    expect(mockClient.updatePlatformConfig).toHaveBeenCalledWith(1, { key: 'val' });
+    expect(mockClient.updatePlatformConfig).toHaveBeenCalledWith(1, {
+      name: 'cfg',
+      value: { key: 'val' },
+    });
   });
 });
diff --git a/src/core/platformconfig/platformconfig.test.ts b/src/core/platformconfig/platformconfig.test.ts
index 307e1c6a..ef37fb56 100644
--- a/src/core/platformconfig/platformconfig.test.ts
+++ b/src/core/platformconfig/platformconfig.test.ts
@@ -22,11 +22,81 @@ describe('platformconfig', () => {
     expect(result.data).toEqual({ id: 1, key: 'val' });
   });
 
-  it('should update platform config', async () => {
-    const value = { setting: true };
-    mockClient.updatePlatformConfig.mockResolvedValue({ id: 1, setting: true });
-    const result = await updatePlatformConfig(mockClient as any, { id: 1, value });
-    expect(mockClient.updatePlatformConfig).toHaveBeenCalledWith(1, value);
-    expect(result.data).toEqual({ id: 1, setting: true });
+  it('should fetch the current config, merge the new value, and PUT without id', async () => {
+    mockClient.getPlatformConfig.mockResolvedValue({
+      id: 22,
+      name: 'experiment_form_max_secondary_metrics',
+      value: '20',
+    });
+    mockClient.updatePlatformConfig.mockResolvedValue({
+      id: 22,
+      name: 'experiment_form_max_secondary_metrics',
+      value: '30',
+    });
+
+    const result = await updatePlatformConfig(mockClient as any, { id: 22, value: '30' });
+
+    expect(mockClient.getPlatformConfig).toHaveBeenCalledWith(22);
+    // name comes from GET; id stays out of the body (URL path).
+    expect(mockClient.updatePlatformConfig).toHaveBeenCalledWith(22, {
+      name: 'experiment_form_max_secondary_metrics',
+      value: '30',
+    });
+    expect(result.data).toEqual({
+      id: 22,
+      name: 'experiment_form_max_secondary_metrics',
+      value: '30',
+    });
+  });
+
+  it('should accept any JSON value for value (string, number, object)', async () => {
+    mockClient.getPlatformConfig.mockResolvedValue({ id: 1, name: 'numeric_cfg', value: 0 });
+    mockClient.updatePlatformConfig.mockResolvedValue({ id: 1, name: 'numeric_cfg', value: 42 });
+
+    await updatePlatformConfig(mockClient as any, { id: 1, value: 42 });
+
+    expect(mockClient.updatePlatformConfig).toHaveBeenCalledWith(1, {
+      name: 'numeric_cfg',
+      value: 42,
+    });
+  });
+
+  it('should throw a malformed-payload error if GET returns a non-object', async () => {
+    mockClient.getPlatformConfig.mockResolvedValue(null);
+    mockClient.updatePlatformConfig.mockClear();
+
+    await expect(updatePlatformConfig(mockClient as any, { id: 999, value: 'x' })).rejects.toThrow(
+      /malformed payload.*got null/
+    );
+    expect(mockClient.updatePlatformConfig).not.toHaveBeenCalled();
+  });
+
+  it('should wrap GET errors with context and not attempt a PUT', async () => {
+    const cause = new Error('network down');
+    mockClient.getPlatformConfig.mockRejectedValue(cause);
+    mockClient.updatePlatformConfig.mockClear();
+
+    await expect(updatePlatformConfig(mockClient as any, { id: 7, value: 'x' })).rejects.toThrow(
+      /failed to fetch existing config/
+    );
+    expect(mockClient.updatePlatformConfig).not.toHaveBeenCalled();
+  });
+
+  it.each([
+    ['null', null],
+    ['false', false],
+    ['zero', 0],
+    ['empty string', ''],
+    ['empty array', []],
+  ])('should accept falsy JSON value: %s', async (_label, falsyValue) => {
+    mockClient.getPlatformConfig.mockResolvedValue({ id: 1, name: 'cfg', value: 'old' });
+    mockClient.updatePlatformConfig.mockResolvedValue({ id: 1, name: 'cfg', value: falsyValue });
+
+    await updatePlatformConfig(mockClient as any, { id: 1, value: falsyValue });
+
+    expect(mockClient.updatePlatformConfig).toHaveBeenCalledWith(1, {
+      name: 'cfg',
+      value: falsyValue,
+    });
   });
 });
diff --git a/src/core/platformconfig/platformconfig.ts b/src/core/platformconfig/platformconfig.ts
index 224ed7c6..7b8a0283 100644
--- a/src/core/platformconfig/platformconfig.ts
+++ b/src/core/platformconfig/platformconfig.ts
@@ -20,13 +20,32 @@ export async function getPlatformConfig(
 
 export interface UpdatePlatformConfigParams {
   id: number;
-  value: Record<string, unknown>;
+  value: unknown;
 }
 
 export async function updatePlatformConfig(
   client: APIClient,
   params: UpdatePlatformConfigParams
 ): Promise<CommandResult<unknown>> {
-  const data = await client.updatePlatformConfig(params.id, params.value);
+  let current: unknown;
+  try {
+    current = await client.getPlatformConfig(params.id);
+  } catch (err) {
+    throw new Error(`Cannot update platform config ${params.id}: failed to fetch existing config`, {
+      cause: err,
+    });
+  }
+  if (!current || typeof current !== 'object') {
+    const got = current === null ? 'null' : typeof current;
+    throw new Error(
+      `Cannot update platform config ${params.id}: GET returned malformed payload (expected object, got ${got})`
+    );
+  }
+  // Last-writer-wins on every field except `value`: we read the current config and PUT it back
+  // with the new value. Concurrent writes to other fields between this GET and PUT are silently
+  // overwritten with the stale read. id is in the URL path; don't echo it in the body.
+  const { id: _id, ...rest } = current as Record<string, unknown>;
+  const merged: Record<string, unknown> = { ...rest, value: params.value };
+  const data = await client.updatePlatformConfig(params.id, merged);
   return { data };
 }