OAuth fails with "Invalid authorization request" at mcp.notion.com/authorize

### MCP server URL

mcp.notion.com

### Where does the issue occur?

When pressing the Connect button

### Transport used

streamable-http

### Client registration type

My server does not have auth

### SSE only: Does your server return the expected status code for POST requests?

Not applicable (my server does not use SSE)

### When did you last reproduce this?

2026-08-05, ~12:40 JST

### Browser and OS

Chrome, macOS

### Describe the issue

The Notion connector disappeared from my connected connectors. When I try to reconnect (both via the directory and as a custom connector), the OAuth flow fails immediately at `https://mcp.notion.com/authorize?response_type=code&client_id=https%3A%2F...` with the plain-text error "Invalid authorization request".

- Happens on both Claude Desktop and claude.ai web
- Other connectors (Gmail, Google Drive, etc.) work fine
- I can connect to the same Notion workspace from ChatGPT's Notion integration without any issue, so Notion's OAuth server itself is working
- Tried: deleting and re-adding the connector, restarting the app, disabling ad blocker, incognito window

### Issue details

```shell
**MCP server URL or name:** mcp.notion.com

**How are you connecting:** Both from the MCP server directory and as a custom connector (https://mcp.notion.com/mcp)

**Where does the issue occur:** In the authorization screen

**When did you last reproduce this:** 2026-08-05, ~12:40 JST

**Browser and OS:** Chrome, macOS (Claude Desktop + claude.ai web)

**Description:**
The Notion connector disappeared from my connected connectors. When I try to reconnect, the OAuth flow fails immediately at `https://mcp.notion.com/authorize?response_type=code&client_id=https%3A%2F...` with the plain-text error "Invalid authorization request".

- Happens on both Claude Desktop and claude.ai web
- Other connectors (Gmail, Google Drive, etc.) work fine
- I can connect to the same Notion workspace from ChatGPT's Notion integration without any issue, so Notion's OAuth server itself is working
- Tried: deleting and re-adding the connector, restarting the app, disabling ad blocker, incognito window

### Expected behavior

The authorize URL should show Notion's OAuth consent screen, and after approving, the Notion connector should appear as "Connected" in Claude's connector settings.

### Logs from your server

```shell

```

### Additional context

_No response_