# X_MAIL_PREVIEW_INVALID

## Means

a mail's declared preview fails its own input schema

## Typical cause

defineMail was given a preview the mail's input schema refuses, so the one render a person checks a template by is of data the mail can never be sent

## Fix

`x mail preview <id> --json` — names the field; then correct preview in the defineMail call to match input

[Mail](/error-codes#mail)