# Writing (/run/troubleshooting/writing) Fix a create or an update that Marfa refuses. Marfa refuses a write it can't apply safely, and changes nothing. The answer's `code` and `details` say why. [Write safely](/build/write-safely) explains the rules a write follows. ## 409 version_conflict [#409-version_conflict] Your write changed a field that someone else also changed since the version you read. Marfa refuses your write rather than overwrite theirs. It sends the item as it is now in `current`, and the version you read in `ancestor`. Combine your change with `current`, and send it again naming `current.version`. Or send the write with `conflict=auto` and let the type's rules settle it. ## 409 ancestor_unavailable [#409-ancestor_unavailable] Marfa no longer keeps a snapshot of the version your write names, so it can't tell what changed since. Housekeeping thins old snapshots, and a version that never existed has none. Read the item again and apply your change to it. [Versions](/versions) explains the history Marfa keeps. ## 400 missing_required_field: version is required [#400-missing_required_field-version-is-required] An update must name the version it read, so Marfa can tell whether the item changed in between. Read the item, and send its `version` with the update. ## 400 validation_error: The request body must be JSON [#400-validation_error-the-request-body-must-be-json] The request has a body but no `Content-Type: application/json` header. Add the header. With `curl`, that's `-H "Content-Type: application/json"`. ## 400 validation_error: Unknown query parameter [#400-validation_error-unknown-query-parameter] The request names a query parameter the operation doesn't take, often a misspelled filter. Marfa refuses it so that a typo can't return everything, and the message lists the parameters the operation takes. Correct the name. Marfa ignores a parameter whose name starts with `_`, so use that for one of your own, such as a cache buster. ## 400 validation_error: Must not contain a lone surrogate [#400-validation_error-must-not-contain-a-lone-surrogate] A string or a property name in the body holds half of a character that takes two UTF-16 code units, such as an emoji cut in the middle. UTF-8 can't carry it. `details.errors[].path` names the text by its JSON pointer. Cut text between characters, not between code units. In JavaScript, `isWellFormed()` checks a string, and `toWellFormed()` replaces each stray half with U+FFFD. ## 400 invalid_properties [#400-invalid_properties] The item's properties don't fit its type: a required field is missing, or a value has the wrong shape. `details.errors` names each field and what is wrong with it. A `core.task`, for example, needs a `title`. Read the type's fields with `marfa types get `, and send what it asks for. [Field kinds](/catalog/field-kinds) gives each kind's rules. Two of them refuse values that look valid: * A whole number that Marfa wouldn't serve back with the same digits, such as `1500000000000000001`. The message starts `Must be a whole number that Marfa serves back with the same digits`. Send it as a string. * A `url` value that the WHATWG URL Standard refuses, such as a host with a forbidden character.