keyValidator._parse Error in push_text_message Function

[4geru]

MCP LINE Bot Server Issue Report

Problem Description

The push_text_message function in the LINE Bot MCP Server (@line/line-bot-mcp-server@0.3.1) is failing with a validation error.

Error Details

• Error Message: MCP error -32603: keyValidator._parse is not a function
• Affected Function: mcp__line-bot__push_text_message
• MCP Server Version: @line/line-bot-mcp-server@0.3.1

Environment

• Platform: Linux 6.8.0-1030-azure
• Working Directory: /workspaces/supabase-line-handson-series
• MCP Configuration: Properly configured in .mcp.json with valid tokens

Configuration

{
  "mcpServers": {
    "line-bot": {
      "type": "stdio",
      "command": "npx",
      "args": [
        "-y",
        "@line/line-bot-mcp-server@latest"
      ],
      "env": {
        "CHANNEL_ACCESS_TOKEN": "[REDACTED]",
        "DESTINATION_USER_ID": "[REDACTED]"
      }
    }
  }
}

What Works

• mcp__line-bot__get_message_quota - Returns correct quota information: {"limited":200,"totalUsage":6}
• Direct LINE API calls work perfectly
• MCP server starts without errors

What Doesn't Work

• mcp__line-bot__push_text_message - Fails with validation error
• Cannot send messages through MCP interface

Reproduction Steps

1. Configure LINE Bot MCP server with valid credentials
2. Attempt to call mcp__line-bot__push_text_message
3. Error occurs: keyValidator._parse is not a function

Workaround

Direct LINE API calls work as expected:

curl -X POST 'https://api.line.me/v2/bot/message/push' \
-H 'Content-Type: application/json' \
-H 'Authorization: Bearer [TOKEN]' \
-d '{
  "to": "[USER_ID]",
  "messages": [{"type": "text", "text": "Test message"}]
}'

Expected Behavior

The push_text_message function should accept parameters and send messages via LINE Bot API without validation errors.

Impact

• Cannot use MCP interface for LINE message sending
• Forces fallback to direct API calls
• Breaks automation workflows that depend on MCP

Suggested Investigation

• Check parameter validation logic in the MCP server
• Verify keyValidator implementation
• Review function signature and parameter requirements

[4geru]

/mcp command on claude code.

│ Manage MCP servers                                                                                                                            │
│                                                                                                                                               │
│ ❯ 1. line-bot  ✔ connected · Enter to view details                                                                                            │
│                                                                                                                                               │
│ MCP Config locations (by scope):                                                                                                              │
│  • User config (available in all your projects):                                                                                              │
│    • /home/codespace/.claude.json                                                                                                             │
│  • Project config (shared via .mcp.json):                                                                                                     │
│    • /workspaces/supabase-line-handson-series/.mcp.json                                                                                       │
│  • Local config (private to you in this project):                                                                                             │
│    • /home/codespace/.claude.json [project: /workspaces/supabase-line-handson-series]                                                         │
│                                                                                                                                               │
│ For help configuring MCP servers, see: https://docs.anthropic.com/en/docs/claude-code/mcp                                                     │
╰───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯
   Esc to exit

[4geru]

I can use quote tool

● LINE MCP を使って API 上限を調べます。
  ⎿  {                           
       "limited": 200,
       "totalUsage": 7
     … +1 line (ctrl+r to expand)

● 現在の LINE Bot API の使用状況：
  - 月間制限: 200メッセージ
  - 使用済み: 7メッセージ
  - 残り: 193メッセージ

[netcaster1]

we got same error message as well when ran the version.
Looks the issue is that Zod 4.x has breaking changes from Zod 3.x. The _parse method was changed to parse in Zod 4.x
Downgraded Zod from v4.0.17 to v3.25.76 and it works. and you also need to updated package.json to prevent future upgrade to v4.x until we get official fix.

[4geru]

Thank you I found the issue.
modelcontextprotocol/typescript-sdk#555

[eucyt]

Thank you for your investigating 🙏
Since it looks like the upgrade of Zod is included in @modelcontextprotocol/sdk v2, we’ll wait for that and then update the Zod version in line-bot-mcp-server to v4.
In the meantime, let’s downgrade zod.

modelcontextprotocol/typescript-sdk#809

[eucyt]

@4geru @netcaster1

We have just released including the corrected Zod version.
Please use this updated version.

https://github.com/line/line-bot-mcp-server/releases/tag/v0.3.2

I'm sorry for the inconvenience caused.