API-create-a-data-source and API-update-a-data-source return invalid_request_url — database creation unreliable + missing POST /v1/databases tool

[Odinn-partners]

Summary

While building a CRM on top of the Notion MCP server, we encountered three distinct issues that make database management through the MCP unreliable:

1. API-create-a-data-source returns HTTP 400 invalid_request_url on every call, yet occasionally creates the database anyway (inconsistent side-effect)
2. API-update-a-data-source returns HTTP 400 invalid_request_url consistently — database properties can never be updated via MCP
3. API-patch-block-children only supports paragraph and bulleted_list_item block types — child_database and most other Notion block types are not supported

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Environment

• MCP server: @makenotion/notion-mcp-server (official)
• Notion API version used by MCP: 2025-09-03
• Integration type: Internal integration (bot)
• Workspace plan: Notion Plus
• Client: Claude Code (claude-sonnet-4-6)

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Issue 1 — API-create-a-data-source returns invalid_request_url but sometimes creates the database

Steps to reproduce

{
  "parent": { "page_id": "311804f8-2911-8032-8eb6-dc30052e7bbd" },
  "title": [{ "type": "text", "text": { "content": "Test DB" } }],
  "properties": {
    "Name": { "title": {} }
  }
}

Expected behavior

HTTP 200 with the created database object.

Actual behavior

{
  "status": 400,
  "object": "error",
  "code": "invalid_request_url",
  "message": "Invalid request URL.",
  "request_id": "..."
}

During our session, the first call created the database despite returning 400. All subsequent calls (6+ attempts, varying payload size and page_id format) returned 400 and created nothing. The behavior is non-deterministic — the database was created as a side-effect of a failing request.

Root cause hypothesis

The MCP server appears to call a URL like /v1/data-sources instead of the standard POST /v1/databases. The Notion API returns invalid_request_url because /v1/data-sources does not exist. The one successful creation may have been a retry hitting the correct endpoint, or a race condition.

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Issue 2 — API-update-a-data-source returns invalid_request_url consistently

Steps to reproduce

{
  "data_source_id": "<valid-database-id>",
  "properties": {
    "New Field": { "rich_text": {} }
  }
}

Expected behavior

HTTP 200 with updated database object (equivalent to PATCH /v1/databases/{id}).

Actual behavior

{
  "status": 400,
  "object": "error",
  "code": "invalid_request_url",
  "message": "Invalid request URL."
}

This completely blocks any post-creation property management via MCP.

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Issue 3 — API-patch-block-children only supports 2 block types

Description

The children parameter of API-patch-block-children is typed as:

anyOf: [paragraphBlockRequest, bulletedListItemBlockRequest]

This means only paragraph and bulleted_list_item can be appended. Notably missing:

• child_database (which would have served as a workaround for Issue 1)
• heading_1, heading_2, heading_3
• numbered_list_item, toggle, callout, divider, image, code

The Notion API supports 20+ block types — the MCP exposes only 2.

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Workaround

We bypassed the MCP entirely by calling POST /v1/databases directly via Node.js HTTPS using the integration token — which worked correctly with Notion-Version: 2022-06-28.

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Suggestions

1. Rename API-create-a-data-source → API-create-a-database and map it to POST /v1/databases (not /v1/data-sources)
2. Rename API-update-a-data-source → API-update-a-database and map it to PATCH /v1/databases/{id}
3. Expand API-patch-block-children to support all block types documented in the Notion API
4. If "data source" is intentional (Notion AI feature), add a separate API-create-a-database tool for the standard database creation endpoint

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Discovered while building a CRM with Claude Code using the official Notion MCP server. Happy to provide the full session log if useful.