[bug] Notion MCP notion-update-page update_properties: relation property rejects valid single-page URL

[bug] Notion MCP notion-update-page update_properties: relation property rejects valid single-page URL with "Invalid page URL"

Summary

When using update_properties on mcp__claude_ai_Notion__notion-update-page to set a relation property to a single page URL, the call fails with Invalid page URL. The URL is valid (verified by directly fetching that page).

Steps to reproduce

1. Find a Notion DB row with a relation property currently linking 2+ pages.
2. Try to reduce the relation to a single page by calling:

``
notion-update-page
command: update_properties
payload: { "<relation_property>": "https://www.notion.so/<valid-page-url>" }
``

1. Observe: Invalid page URL validation error, despite the URL being well-formed and pointing to an existing page.

Expected behavior

Relation property is updated to contain only the specified single page.

Actual behavior

Invalid page URL error. The MCP server appears to incorrectly validate single-value relation updates.

Environment

• Tool: mcp__claude_ai_Notion__notion-update-page (Anthropic-hosted Notion connector via Claude.ai)
• Discovered via Claude Code (CLI), 2026-04-14
• Specific case: tenant master DB cleanup, reducing relation from 2 → 1
• OS: macOS Darwin 24.6.0

Workaround (confirmed working)

Two-step:

1. Set relation to empty array first: { "<relation_property>": [] }
2. Then set to desired single value: { "<relation_property>": [{ "id": "<page-id>" }] }

Both steps succeed. The intermediate empty state is brief but should be performed atomically when possible to avoid data inconsistency.

Related

• Bug 1 (replace_content prefix collision): see separate issue
• Internal manual: docs/rules/notion-mcp-bugs.md (Korean)