9: FailedToParse

What does it mean?

The server could not parse the submitted command, query or expression. The structure is syntactically invalid or not in the expected format.

Why does it happen?

A malformed JSON/BSON structure, missing or extra fields, incorrect operator usage, invalid aggregation pipeline syntax, or a command document that does not match the expected format.

How to fix it

Correct the command/query/pipeline structure according to the documentation. Validate the JSON structure (missing brackets/commas, wrong field names). Check the syntax of aggregation stages. Make sure operators are used correctly and arguments are supplied in the expected format.