On this page, you will find more information about the most common causes and most relevant solutions for the Notion error '400 "missing_version"'. Do you need help straight away? Visit our support page.
The Notion Labs, Inc. documentation indicates that error code '400 "missing_version"' is caused by the following problem: "The request is missing the required Notion-Version header. See Versioning.".
Do you think there is another cause for this error? Let others know in the comments.