updating or adding multiple values for multi_select properties fails in update-page

[ken5scal]

I'm trying to update a page with a multi_select property.
When adding or updating a single value, it works.
But when adding or updating multiple values, it returns the following errors

• successful failed example01

⏺ notion - Update Notion page (MCP)(data: {"page_id":"c169f193fa344272b9c61b38b25fded3","command":"up
                                   date_properties","properties":{"tags":["anthropic","llm/mcp","oss"
                                   ,"training/education"]}})
  ⎿  Error: MCP error -32602: MCP error -32602: Invalid arguments for tool notion-update-page: [
       {
         "code": "invalid_union",
         "unionErrors": [
           {
             "issues": [
               {
                 "code": "invalid_type",
                 "expected": "string",
                 "received": "array",...

• failed example02

⏺ notion - Update Notion page (MCP)(data: {"page_id":"c169f193fa344272b9c61b38b25fded3","command":"up
                                   date_properties","properties":{"tags":"anthropic,llm/mcp,oss,train
                                   ing/education"}})
 Error: {"name":"APIResponseError","code":"validation_error","status":400,"headers":{},"body":"{\"
     object\":\"error\",\"status\":400,\"code\":\"validation_error\",\"message\":\"Invalid select
     value for property \\\"tags\\\": \\\"anthropic,llm/mcp,oss,training/education\\\". Value must be
     one of the following: \\\"aad\\\", \\\"microsoft\\\", \\\"oss\\\", \\\"red\\\", \\\"osint\\\",
     \\\"confidential_computing\\\", \\\"device_mgt\\\", \\\"architecture\\\", \\\"aws\\\",
     \\\"cncf\\\", \\\"container\\\", \\\"sre\\\", \\\"blue\\\", \\\"dfir\\\", \\\"service\\\",
     \\\"google\\\", \\\"supply_chain\\\", \\\"slsa\\\", \\\"sigstore\\\", \\\"trust\\\",
     \\\"governance\\\", \\\"jwt\\\", \\\"oauth\\\", \\\"digital_identity\\\", \\\"oidc\\\",
     \\\"vul_mgt\\\", \\\"seccamp\\\", \\\"fido\\\", \\\"financial\\\", \\\"github\\\", \\\"cicd\\\",
     \\\"datadog\\\", \\\"observability/detection\\\", \\\"terraform\\\", \\\"edr\\\",
     \\\"windows\\\", \\\"enum\\\", \\\"defcon\\\", \\\"aml\\\", \\\"netflix\\\", \\\"paper\\\",
     \\\"sto\\\", \\\"siem\\\", \\\"soar\\\", \\\"sentinel\\\", \\\"data_science/data_engineer\\\",
     \\\"privacy\\\", \\\"golang\\\", \\\"threat_model\\\", \\\"file_storage\\\", \\\"pac\\\",
     \\\"google_workspace\\\", \\\"blockchain\\\", \\\"ssi\\\", \\\"gitlab\\\", \\\"conf_codeblue\\\",
      \\\"dev\\\", \\\"osquery\\\", \\\"devsecops\\\", \\\"sdlc\\\", \\\"mac\\\", \\\"test\\\",
     \\\"alb\\\", \\\"ecs\\\", \\\"cloudflare\\\", \\\"iac\\\", \\\"mitre\\\", \\\"handbook\\\",
     \\\"pmconf\\\", \\\"research\\\", \\\"odic\\\", \\\"iddance\\\", \\\"利害関係あり\\\",
     \\\"phishing\\\", \\\"training/education\\\", \\\"gocon\\\", \\\"hashiconf\\\", \\\"business\\\",
      \\\"cloudnative_days\\\", \\\"ncsc\\\", \\\"finolab\\\", \\\"slack\\\", \\\"chaos_eng\\\",
     \\\"risk_mgt\\\", \\\"audit\\\", \\\"ossf\\\", \\\"ebpf\\\", \\\"cisa\\\", \\\"data_modeling\\\",
      \\\"serverless\\\", \\\"soc\\\", \\\"kql\\\", \\\"jamf\\\", \\\"career\\\", \\\"nist\\\",
     \\\"patch_mgt\\\", \\\"zta\\\", \\\"microsoft_defender\\\", \\\"mercari\\\", \\\"log4j\\\",
     \\\"threat_intelligence\\\", \\\"cis\\\", \\\"interest:high\\\", \\\"pki\\\", \\\"misc\\\",
     \\\"policy\\\", \\\"space\\\", \\\"book\\\", \\\"products\\\", \\\"GraphQL\\\", \\\"awesome\\\",
     \\\"crypto\\\", \\\"sast\\\", \\\"dast\\\", \\\"robot\\\", \\\"pdm\\\", \\\"cspm\\\",
     \\\"opa\\\", \\\"ipa\\\", \\\"heroku\\\", \\\"dlp\\\", \\\"auth0\\\", \\\"owasp\\\",
     \\\"ditstributed_systems\\\", \\\"ietf\\\", \\\"csa\\\", \\\"jupiterOne\\\", \\\"asset_mgt\\\",
     \\\"csp\\\", \\\"law\\\", \\\"chainguard\\\", \\\"secrets\\\", \\\"my_thought\\\", \\\"cwe\\\",
     \\\"blender\\\", \\\"cg\\\", \\\"連載_戦略としての企業価値\\\", \\\"black_hole\\\", \\\"isac\\\",
      \\\"dfir_半田病院\\\", \\\"やってみた\\\", \\\"attack_surface_mgt\\\", \\\"writing\\\",
     \\\"uem\\\", \\\"sans\\\", \\\"ssvc\\\", \\\"jpcert\\\", \\\"burp\\\", \\\"typescript\\\",
     \\\"dfir_uber\\\", \\\"ctf\\\", \\\"microsoft_ignite_2022\\\", \\\"keynote\\\", \\\"db\\\",
     \\\"design_pattern\\\", \\\"lastpass\\\", \\\"stats\\\", \\\"web_api\\\", \\\"abac\\\",
     \\\"lyft\\\", \\\"dfir_lastpass\\\", \\\"config_mgt\\\", \\\"malware/ransom\\\", \\\"oreilly\\\",
      \\\"freee\\\", \\\"idor\\\", \\\"dns\\\", \\\"gcp\\\", \\\"dfir_circleci\\\",
     \\\"public_comments\\\", \\\"まとめ\\\", \\\"aqua\\\", \\\"llm/ai\\\", \\\"conf_jsac2023\\\",
     \\\"graph_data\\\", \\\"pinterest\\\", \\\"ntt\\\", \\\"dod\\\", \\\"thm\\\", \\\"nisc\\\",
     \\\"family\\\", \\\"ssrf\\\", \\\"conf_blackhat\\\", \\\"nasa\\\", \\\"conf_sans\\\",
     \\\"dfir_okta\\\", \\\"conf_oidc\\\", \\\"enisa\\\", \\\"periodic_reports\\\", \\\"wiz\\\",
     \\\"iam\\\", \\\"splunk\\\", \\\"atp29/midnight_blizzard/nobelium\\\", \\\"crowdstrike\\\",
     \\\"home\\\", \\\"zanzibar\\\", \\\"nsa\\\", \\\"redcanary\\\", \\\"risk\\\",
     \\\"dfir_kadokawa\\\", \\\"ネタ/thoughts/memo\\\", \\\"twitter\\\", \\\"cisco\\\", \\\"jnsa\\\",
     \\\"objective-see\\\", \\\"snyk\\\", \\\"school\\\", \\\"conf_fwd:cloudsec\\\",
     \\\"1password\\\", \\\"まくにか マクニカ\\\", \\\"ioc\\\", \\\"trivy\\\", \\\"kaggle\\\",
     \\\"government\\\", \\\"math\\\", \\\"star\\\", \\\"articaleOfTheDay\\\", \\\"podcasts\\\",
     \\\"Wiz\\\", \\\"Iac\\\", \\\"dfir_dmm\\\", \\\"apache_iceberg\\\", \\\"duckdb\\\", \\\"byMe\\\",
      \\\"elasticsearch\\\", \\\"llm/prompt\\\", \\\"llm/mcp\\\", \\\"dfir_tjactions\\\",
     \\\"flatt\\\", \\\"LayerX\\\", \\\"anthropic\\\", \\\"llm/agent\\\", \\\"obsidian\\\". If a new
     select option is needed, the data source must be updated to add
     it.\",\"request_id\":\"22c4b03e-bbbf-47d8-bb3a-744b39cf7127\"}"}

[onestardao]

Thanks for the clear repro. From the Problem Map, this looks closest to #6 – Logic Collapse & Recovery: the tool arg/validator path accepts a single multi_select value but collapses when it’s an array, so you hit a type-mismatch dead end.

Quick checks to pinpoint it:

Schema vs payload: Notion expects
properties: { "": { "multi_select": [ { "name": "A" }, { "name": "B" } ] } }
Make sure the MCP tool’s update_page schema declares that field as an array of objects, not a single object or string.

Coercion layer: Log the exact JSON your MCP server sends to Notion for the failing case. If you see the array getting stringified or the objects dropped, the bug is in the argument coercion/validator (common when reusing the single-value path).

If you want, I can share a short checklist we use for #6 (schema/asserts, coercion, and request mirroring) to help you zero in quickly.

[ken5scal]

@onestardao thanks but #6 is far different from 'Logic Collapse & Recovery', but permissions.

As I used the curl, the correct format should be as follows, as you said.

% curl -X PATCH \
  https://api.notion.com/v1/pages/c169f193fa344272b9c61b38b25fded3 \
  -H 'Authorization: Bearer {{NOTION_ACCESS_KEY starts with ntn_}}' \
  -H 'Content-Type: application/json' \
  -H 'Notion-Version: 2022-06-28' \
  -d '{
    "properties": {
      "tags": {
        "multi_select": [
          {
            "name": "valueA"
          },
          {
            "name": "valueB"
          }
        ]
      }
    }
  }

I successfully told the correct format to MCP, yet update_properties still fails.
The log from Notion MCP is as follows

⏺ notion - Update Notion page (MCP)(data:
                                   {"page_id":"c169f193fa344272b9c61b38b25fded3","command":"update_properties","properties":{"tags":{"multi_select":[{"name":"valueA"},{"name":"valueB"},{"name":"valueC"},{"name":"valueD"},{"name":"valueE"}]}}})
  ⎿  Error: MCP error -32602: MCP error -32602: Invalid arguments for tool notion-update-page: [
       {
         "code": "invalid_union",
         "unionErrors": [
           {
             "issues": [
               {
                 "code": "invalid_type",
                 "expected": "string",
                 "received": "object",
...

I'm wonderiing how would you do this

Log the exact JSON your MCP server sends to Notion for the failing case

[onestardao]

Thanks for clarifying. You’re correct that from the Notion API’s perspective this shows up as
invalid_union / invalid_type, which points to a schema or permission mismatch.

From the WFGY Problem Map view it still maps to No.6 Logic Collapse & Recovery.
Reason: single-value updates succeed (schema is valid), but the moment multiple values are sent,
the runtime collapses into a dead-end with no fallback. That’s exactly the type of “collapse” we
categorize under No.6.

So the two lenses are:

• API layer → invalid union / type mismatch.
• Problem Map layer → No.6 Logic Collapse (payload structure collapses under multiple values).

Practically the fix is to log the exact JSON your MCP server sends and ensure the field is serialized
as an array of objects, e.g.:

"multi_select": [
  { "name": "value1" },
  { "name": "value2" }
]

rather than a single object or incorrectly flattened structure.

Reference: WFGY Problem Map – No.6 Logic Collapse & Recovery

https://github.com/onestardao/WFGY/tree/main/ProblemMap/README.md

[ken5scal]

Oh, you were referring to your OWN framework.

[onestardao]

Yes, it's effective it's reasoning layer, no need to change infra, but powerful (every devs have triied and told me this)